The 1837 edition changed the relative pronoun which to who. However, the following singular verb was was kept, which makes it seem like there was only one person in the band (“who was appointed”). One could suppose that the who was refers to Gid rather than to the band, although that too seems odd. If the who is to be retained in the standard text, the was should probably be changed to were.
One question here is whether band should be considered a unity or a group of individuals. Earlier, under Mosiah 23:25, I considered whether army should be semantically viewed as a singular or a plural. Under Alma 43:35, I considered whether the relative pronoun who can be used to refer to army. Those analyses suggest that for Alma 57:29 the standard text could read either as “the band which was appointed” (where band is treated as a unity) or as “the band who were appointed” (where band is treated as a group of individuals). The critical text will, of course, restore the original reading, “the band which was appointed”, but with the understanding that either of the two interpretations is possible.
For some other cases of band, a change of the relative pronoun which to who after band was marked by Joseph Smith in the printer’s manuscript. The use of who is semantically appropriate when the text refers to making a covenant:
There is one example in the earliest text where who rather than which refers to the members of a band making a covenant:
But there are two cases where the 1837 change from which to who seems inappropriate:
In Helaman 6:18 the band, not its individuals, was formed by Kishcumen and Gaddianton. In Helaman 11:2, because of the preceding robbers, Joseph Smith interpreted the which as referring to the individual robbers rather than to the band itself, but the emphasis in this case seems to be on the band itself as the source of “this work of destruction and wickedness”. There is one case in the text that refers to a band acting as a unity where an original which has been left unchanged:
In the critical text, which will be restored in all those cases involving grammatical emendation, no matter whether the relative pronoun refers to the band as a unity or as a group of individuals. For further discussion, see under which in volume 3.
Summary: Restore the original which in Alma 57:29 (“the band which was appointed to guard them down to that land”); also maintain the original singular verb form was; even though the original text reads which was in this passage, the word band can be interpreted as either a unity or a group of individuals; similarly, other uses of which in reference to a band will be either restored or maintained in accord with the reading of the earliest textual sources.