Consider the following quotes made by ancient scholars and modern LDS leaders
Everything changes and nothing stands still.
The world changes constantly and dramatically, but God, His commandments, and promised blessings do not change. They are immutable and unchanging.
The Lord does not want His church to become root bound and stagnant. Constant revelation through the prophets is needed for the growth of His kingdom.
There is nothing so unchanging, so inevitable as change itself.
Changes made in the early Christian church are defined as apostasy by the LDS faith. This apostasy involves two parts: 1) Changing of important teachings or doctrine and 2) A loss of priesthood authority. The latter (loss of priesthood authority) cannot be proven and is simply assumed. However, the doctrine did in fact evolve and get clarified over time, and this can be shown in the historical record which remains.
When the Church of Christ was established formally in Apr 1830, they claimed that the apostasy had been in force for 1500 years. Priesthood was claimed by this new church, though the explanation of the method by which this authority came evolved in the early church. The offices also evolved, with the Melchizedek priesthood being introduced around June of 1831. By 1835, many of the offices were in place and although changes in details including the age of ordination and structure of the quorums continue, the pace of change has slowed considerably.
Change within early Christianity – Infant baptism
An early justification within Mormonism to prove the apostasy of the Catholic church was the introduction of the practice of infant baptisms. Parley P. Pratt explained:
The Catholic Church profess to be the true Church—the ground and pillar of the truth, handed down by regular succession from the ancient Church, of which they are still members; and their priesthood and apostles are now of the very same Church which the New Testament calls the true Church at Rome… If they are what they profess to be, every one of them have been buried with Christ in baptism, and have risen again to newness of life. We will, however, leave them to describe whether that is really the case, or whether they are contented to sprinkle a few drops of water on an infant’s face and call that a burial! […] Have these modern Roman Catholics gone forward repenting of their sins, and been buried in water, in the likeness of the death of Jesus Christ according to this pattern? If they have not, they are a spurious Church of Rome, and not real. 
Joseph Fielding Smith later clarified this view in his book Essentials in Church History. In a section about the apostasy and the rise of Rome, he wrote:
The ordinance of baptism was changed from burial in the water for the remission of sins, to sprinkling of a little water on the head. Sprinkling of infants, miscalled baptism, a custom which “is mockery before God, denying the mercies of Christ, and the power of the Holy Spirit,” became a fixed and universal custom.
Historically, infant baptisms began to be practiced around 200 AD and became fully established about 2 centuries later.
Such a significant change could be described in various terms within Mormonism, and would likely fall into one of the following categories:
- A change in policy
- A change in doctrine
- Modern Revelation
In the above quote, Pratt makes the case that this change is a change of doctrine. As the LDS faith has a core belief that doctrine is eternal, to change doctrine is a sure sign of apostasy.
Change within Mormonism – Washings in the temple
As part of the early temple ceremonies, participants would cleanse themselves prior to receiving their new name and endowments. This cleansing had at least 2 components:
- The person would be re-baptized no more than a week prior to entering the temple to receive a remission of sins so that they would be clean to enter.
- The person would take off all of their clothing and be washed (with a scrub brush) by someone of their same sex in a bathtub so that they were clean. During this washing the person performing the ordinance would say some words which included a series of blessings.
To paraphrase Pratt, “The early saints were not contented to sprinkle a few drops of water on an participant’s face and call that a washing”. However, sometime between about 1920 and 1933, this ordinance was changed. Washing became more symbolic and consisted of a few drops of water placed on different parts of one’s body. Immersion was gone. Bathtubs were removed from the temples. The ordinance was changed again in 2005 when participant began wearing undergarments during this procedure rather than the open covering that was used up to that point. The ceremony had changed yet again.
Changing this exalting ordinance from one of fully immersion to sprinkling closely parallels the changes to baptism made within Catholicism.
Were these changes:
- A change in policy?
- A change in doctrine?
- Modern revelation?
In the case of Mormonism, a believer would tend to frame this change as an example of modern revelation in spite of the parallel to earlier changes made in the Catholic church.
The end of plural Marriage
Mormonism teaches that the apostasy of the early Christian church was prophesied by early church leaders and that this is one sure way to know that it occurred. There are at least 4 prominent LDS leaders of the Quorum of the 12 or First Presidency who have in effect prophesied that the church would not end the practice of plural marriage at least until the 2nd coming of Christ.
Heber C. Kimball of the 1st presidency stated:
[Plural marriage]…would end he said when the Church had gone to the Devil or the Priesthood taken from this people – then God would give it to another people.
“The principle of plurality of wives never will be done away…”
“You might as well deny ‘Mormonism,’ and turn away from it, as to oppose the plurality of wives.”
Apostle George Teasdal stated:
I bear my testimony that it is a necessity, and that the Church of Christ in its fullness never existed without it. Where you have the eternity of marriage you are bound to have plural marriage; bound to; and it is one of the marks of the Church of Jesus Christ in its sealing ordinances.
John Taylor, the 3rd president of the church stated:
I the Lord do not change and my word and my covenants and my law do not, and as I have heretofore said by my servant Joseph: All those who would enter into my glory must and shall obey my law. And have I not commanded men that if they were Abraham’s seed and would enter into my glory, they must do the works of Abraham. I have not revoked this law, nor will I, for it is everlasting, and those who will enter into my glory must obey the conditions thereof; even so, Amen.
Wilford Woodruff, 4th president of the church stated in 1888:
We are not going to stop the practice of plural marriage until the Coming of the Son of Man.
In 1890, the practice was officially abandoned in the United States with the issuance of what would become Official Declaration 1.
Were these changes:
- A change in policy?
- A change in doctrine?
- Modern Revelation?
Is it a change in policy?
Ceasing to practice polygamy could be framed as a change in policy, since the core doctrine remains intact and canonized in section 132. Indeed, when Official Declaration 1 was implemented, it was only intended for the United States. Plural Marriages in Mexico continued to be performed for about 15 years after 1890.
However, polygamy itself is not and was not a policy. It has been clearly defined as being an eternal doctrine. Thus, if a change in policy occurred, it could only be defined as the policy regarding how the doctrine is practiced. The line between policy and doctrine becomes thin and blurred in this case.
Is it a change in doctrine?
The doctrine of polygamy, as described by Joseph Smith in 1842, publically preached since 1852, and published in the LDS scriptures since 1876 remains canonized. However, an interview in 1998, Gordon B. Hinkley stated:
I condemn it, yes, as a practice, because I think it is not doctrinal. It is not legal. And this church takes the position that we will abide by the law.
In a lesson manual about section 132 (the revelation justifying polygamy), the lesson notes state:
Plural marriage – The following information is provided to help you address questions class members may have about the practice of plural marriage. This topic should not be the focus of the lesson.
So while it is clear that the doctrine of plural marriage was not changed by the first Manifesto, it is being deemphasized today with at least some church leaders calling the practice non-doctrinal.
Is it Modern Revelation?
The introduction of the practice of plural marriage was not considered to be a modern revelation. It was considered to be a restoration of Gods law that had been taken from the earth due to the evil system of monogamy popularized by the Romans. On the other hand, cessation of the practice of polygamy has been framed in terms of modern revelation by many church leaders.
Apostasy during the restoration
The early mormon church was on the move. In each geographic location that it was headquartered, a different church doctrine emerged. Each location had followers which considered the next locations doctrines and practices to represent apostasy. In every case, significant changes in doctrine caused the church to splinter. The group that had changed claimed “continuing revelation” and the group remaining with the original teachings claimed that the other group had apostatized. A few examples:
The early New York period
This period was characterized by the use of seer stones, abundant speaking in tongues, and revelations by all members. There was a high level of participation and democracy within the movement. Both the Whitmers and Hyrum Page (their son-in-law) had their own seer stones. These early members mostly broke from the main branch of the church by 1838. While they did not form church with a significant following, David Whitmer concluded that all revelations received without the use of seer stones were of the devil.
The Kirtland Era
The Kirtland period was characterized by a simple temple ceremony including washings and anointings, the establishment of a priesthood hierarchy, and teaching regarding the corporal nature of God and the 3-member godhead. The Community of Christ, reorganized around 1860 was based on the model of Mormonism created during the Kirtland Era, one which rejected polygamy.
The Missouri Era
One focus of the Missouri saints was on the impending return of the savior (to Missouri). Several branches of the LDS movement remained in Missouri. Branches formed with Missouri as a center-place include the Cutlerites (Church of Jesus Christ) and various branches of the Church of Christ (Temple Lot).
The Nauvoo Era
The Nauvoo period brought new practices including baptism for the dead and a new temple endowment based in part on masonic rituals. Associated with these new temple rituals was the practice of plural marriage which soon became one of the defining characteristics of the movement.
Both the introduction and cessation of the practice of polygamy within the LDS movement caused splintering. The introduction met resistance from Emma Smith and William Law (among others) and arguably led to the creation of the True Church of Jesus Christ of Latter Day Saints and the Community of Christ, the 2nd largest branch in the LDS movement. When the practice or doctrine was discontinued, no fewer than about 18 denominations have been formed in various ways to continue the practice. As this was a core doctrine, the change sent shockwaves through the movement and a splintering was perhaps inevitable.
Does change in general constitute a change in policy, doctrine, modern revelation, or apostasy?
In a word, YES. It constitutes any or all of these depending on your perspective. The only thing that we can be certain of is that change will continue. Organisms that change rapidly are more likely to survive. This may not be the case with organizations, as some data suggests that mainstream churches are losing more members than conservative movements. Mormonism, with its gerontocracy has been and will likely continue to be a conservative movement which changes slowly. And depending on your perspective, this means that it is either experiencing a slow rate of apostasy or a rather limited amount of modern revelation.
 Heraclitus of Ephesus, as quoted by Plato
 Elder L. Tom Perry, “Obedience to Law Is Liberty”
 Progress through Change, Marvin J. Ashton – https://www.lds.org/general-conference/1979/10/progress-through-change?lang=eng
 Palmyra Reflector, 14 Feb. 1831.
 Power from on High, Greg Prince, pg 18 http://signaturebookslibrary.org/power-from-on-high-01-2/
 On 1 Feb, 1849 – First counselor Heber C. Kimball related this in a Sunday meeting. See: The Mormon Hierarchy: Extensions of Power, Quinn 1997. See also: http://www.exmormon.org/mormon/mormon036.htm
 Apostle Heber C. Kimball, Deseret News, November 7, 1855
 Apostle Heber C. Kimball, Journal of Discourses, v. 5, p. 203
 Apostle George Teasdale (quorum of the 12 from 1882-1907), Journal of Discourses, v. 25, pp. 19-22
 LDS Church Authority and New Plural Marriages, 1890 – 1904, D. Michael Quinn – https://www.dialoguejournal.com/wp-content/uploads/sbi/issues/V18N01.pdf
 See Apostle George Teasdale (quorum of the 12 from 1882-1907), Journal of Discourses, v. 25, pp. 19-22 and D&C section 132.
 Whitmer, An Address to All Believers in Christ…(Richmond, Mo.: David Whitmer, 1887), 54.