In the original text, this passage begins with a singular pronoun he but makes an unexpected transition to the plural they, then reverts to he in verse 11, and finally returns to they a second time. Joseph Smith systematized the pronouns here so that verse 10 is consistently singular and verse 11 is consistently plural. The original text, however, shows a parallel pattern of generic singular (parts A and B) followed by generic plural (part C):
A verse 10 and therefore he that will harden his heart the same receiveth the lesser portion of the word and he that will not harden his heart
verse 11 and he that will harden his heart
B verse 10 to him is given the greater portion of the word until it is given unto him to know the mysteries of God
verse 11 to him is given the lesser portion of the word
C verse 10 until they know them in full
verse 11 until they know nothing concerning his mysteries
Switching the number for generic pronouns within the same passage is fairly common in the original text; see the other examples listed under 1 Nephi 10:18–19. The critical text will restore the original, repeated pattern of generic singular he /his /him followed by generic plural they here in Alma 12:10–11.
In verse 10, Joseph Smith’s editing of “until they know” to “until he know” shows him creating a distinctive subjunctive use of he know rather than the indicative he knoweth or he knows. In most contexts where we can distinguish between subjunctive and indicative verb forms in until- clauses, the Book of Mormon text prefers the indicative, as in “until the time cometh” (in 2 Nephi 9:2 and Ether 3:21), 18 times in all. But the original text also has a few distinctive cases of the subjunctive in until-clauses (the first one quotes Isaiah 6:11):
Thus Joseph’s minimal editing of “until they know” to “until he know” can be supported by usage elsewhere in the text. (The example in Ether 2:11 was edited in the 1837 edition to a different subjunctive form, “until the fullness come”; see the discussion under that passage.)
Summary: Restore the original pronominal variation in Alma 12:10–11; switches in pronominal number are found elsewhere in the original text.