If two identical twins with very similar personalities followed AYP protocol but one used some other nice mantra like "soham" instead of Iam and they both made lovely progress for the next 40 years and then got together again, would their choice of mantras resulted in distinctive personality differences or different chakra emphasis, etc?
Well, identical twins do not start out identical, so there's no way of knowing. Of course, science will tell you they do, and identical upbringing has a big effect, but those twins have huge differences in their karma that would make the real difference in their personalities. Sorry this doesn't answer your specific question, which was hypothetical about mantra effectiveness.
interesting...I have heard before that usually one twin is more "evoloved" (for lack of a better word) than the other & may likely serve to assist the other with their karmic burden...or at least provide energetic support...fascinating ....