I don't see anything wrong with aliorum, which means straightforwardly "of others".
I suppose it's just that I'm used to seeing
alius used with some sort of contrast, where the author mentions one thing and then uses
alius to mark out a different group - 'some people read books, but others prefer computers'. Here 'of others' means just 'people other than myself'. This sense would be conveyed adequately by something like
alicuius.
If the context of the sentence was something like, 'O great Hecate, I know that the Romans are favoured by the gods, and I do not ask for powers to affect them. But grant me the power of altering the memories of others, in order for them to forget certain information upon completion of a specific action.' I would feel a bit more confortable with
aliórum.
I suppose arguably it might be important to emphasise that this power affects other people and can't be used on the self, and maybe
alius would be justified on those grounds - I just can't really think of a parallel for such a use without something like
praeter mé. But it may be that the idiom carries across perfectly well.
Sorry, this is all just a minor quibble - I apologise for stirring up all this fuss over it!