The earliest text here reads “of bringing many of the Zoramites to repentance”. The preposition of is found in the original manuscript. Greg Wright (personal communication, 29 August 2006) suggests that the of in this passage could be an error for in, especially since there are four similar sentences involving the word instrument where the preposition is in (three of these also have the same verb form, bringing):
One could argue that in Alma 35:14 the of entered the text because of the surrounding occurrences of of (“in the hands of God of bringing many of the Zoramites to repentance”).
Even so, there is one other example with the of, although this of is not extant in the original manuscript:
Note that in this last case there are no surrounding of ’s that could have prompted replacing an original in with of. It looks like the of is intended in both Alma 26:15 and Alma 35:14, despite its difficulty for modern readers. The critical text will maintain the occurrence of of in both these passages.
Summary: Maintain the occurrence of of rather than the expected in in Alma 26:15 (“of doing this great and marvelous work”) and in Alma 35:14 (“of bringing many of the Zoramites to repentance”).