Matthew 5:26–27 (King James Bible) thou shalt by no means come out thence … thou shalt not commit adultery
Here we have two instances where LDS editions accidentally replaced thou shalt with thou shall. In the first case, in verse 26, the 1888 large-print edition made the replacement; in the second case, in verse 27, the 1905 missionary edition made the change. The 1888 edition was never used as a copytext, so this typo was not extended to any subsequent editions. The 1911 LDS edition was set from the 1905, so the typo was extended to that edition; but the 1920 LDS edition restored the original thou shalt. In both cases, the corresponding King James text has, as expected, thou shalt, as will the critical text. For further discussion of the tendency to replace thou shalt with thou shall, see under Mosiah 12:11. For another example of this change, see nearby under 3 Nephi 12:33.
Summary: Maintain both instances of thou shalt in 3 Nephi 12:26–27, the reading of the earliest Book of Mormon text and the corresponding King James text.