The chapter headings were written by Bruce R. McConkie and included in the 1979 printing of the LDS format of the KJV. To my knowledge, there was never a vote to accept or deny these chapter headings or other footnotes and maps as canon.

verses 24, Authoritative baptism is required.

2 Wherefore, although a man should be baptized an hundred times it availeth him nothing, for you cannot enter in at the strait gate by the law of Moses, neither by your dead works.

3 For it is because of your dead works that I have caused this last covenant and this church to be built up unto me, even as in days of old.

Therefore, he took Moses out of their midst, and the Holy Priesthood also;
26 And the lesser priesthood continued, which priesthood holdeth the key of the ministering of angels and the preparatory gospel;
27 Which gospel is the gospel of repentance and of baptism, and the remission of sins, and the law of carnal commandments, which the Lord in his wrath caused to continue with the house of Aaron among the children of Israel until John, whom God raised up, being filled with the Holy Ghost from his mother's womb.

Further more, the JST excerpts in the back have no more backing to them than the rest of the footnotes. If the JST were canon, we would read the JST Bible, and not the KJV.

The Book of Mormon was published in 1830, and no additions or changes have been canonized since then, other than those which are intended to correct spelling, punctuation, or grammar