The critical text will allow instances of thou shall rather than thou shalt, providing they are supported by the earliest text. Nonetheless, in some cases, thou shall may represent an early error in the text. For instance, here in Alma 10:7, perhaps the shall was the result of the use of he shall in the next clause. Also note that in the following verse, Amulek refers once more to the language of the angel, but in this case we get the grammatically correct thou shalt:
So the odds are high that the occurrence of thou shall in the earliest textual sources for Alma 10:7 is an error for thou shalt. Even so, the critical text will maintain this instance of thou shall since elsewhere in the text there are examples where such usage appears to be fully intended (see the discussion under Mosiah 12:11).
Summary: Restore in Alma 10:7 the nonstandard use of thou shall, the earliest reading in the text (even though this may be an error for the standard thou shalt).