Good luck to all the candidates in Round 2! For those stressing about the interview, definitely prepare for lots of behavioral questions, I actually felt the CMU interview was among the more challenging b-school interviews for this reason. I also did due diligence on the interviewers, and chose someone who aligned closely with my interests and backgrounds, so I don't think you will get faulted for changing interviewer, just mention it in the interview briefly perhaps, that the more you thought about the importance of this interview, you felt it was wise to pick someone whose background matched more closely, something like that.