While reading a recent book by Russell M. Nelson, I encountered a few comments where it appears that Nelson does not hold to the popular but rather naïve view among many Latter-day Saints that the JST is a pure textual restoration of the Old and New Testaments.
In the JST, “The Gospel According to St.” is changed to “The Testimony of St.” for Matthew and John. Notwithstanding this, Nelson follows the KJV (and the Greek manuscript traditions that have such headings) for at least the Gospel of Matthew:
The word angel is very meaningful. It comes to us from the Greek language. The Greek word ΑΓΓΕΛΟΣ means “messenger.” The same noun is centered in the Greek word for gospel, which is ΕΥΑΓΓΕΛΙΟΝ. Its literal meaning is “good message” or “good news,” with an implication of a heavenly angelic source. ΕΥΑΓΓΕΛΙΟΝ is the very first word in the Greek New Testament (“Gospel According to St. Matthew”). (Russell M. Nelson, Accomplishing the Impossible: What God Does, What We Can Do [Salt Lake City: Deseret Book, 2015], 18-19, emphasis in original)
Elsewhere, discussing JST Matt 6:14 (corresponding to Matt 6:13) where the JST clarifies “lead us not into temptation” by rendering the passage as “And suffer us not to be led into temptation, but deliver us from evil” is understood, not as a textual restoration, but clarification:
The Lord’s Prayer is recorded twice in the New Testament and once in the Book of Mormon. It is also included in the Joseph Smith Translation of the Bible, where clarification is provided by these two phrases:
1. “Forgive us our trespasses as we forgive those who trespass against us,” and
2. “Suffer us not to be led into temptation, but deliver us from evil.”
The clarification on forgiveness is supported by other statements of the Master. He said to His servants, “Inasmuch as you have forgiven one another your trespasses, even so I, the Lord, forgive you” (Doctrine and Covenants 82:1). In other words, if one is to be forgiven, one must first forgive (See Matthew 18:23-25; Doctrine and Covenants 64:10). The clarification on temptation is helpful, for surely we would not be led into temptation by Deity. The Lord said, “Watch and pray, that ye enter not into temptation” (Matthew 26:41). (Ibid., 46, emphasis in bold added; cf. Kevin L. Barney, Joseph Smith and Matthew 6:13)
For a recent scholarly discussion of the JST, see:
Thomas A. Wayment, "Intertextuality and the Purpose of Joseph Smith's New Translation of the Bible" in Mark Ashurst-McGee, Robin Scott Jensen, and Sharlyn D. Howcroft, eds., Foundational Texts of Mormonism: Examining the Early Sources (New York: Oxford University Press, 2018), pp. 74-100.