I have finally got calluses..and I practice chord changes all the tim (still really new)..Ive been trying not to remove the fingers from the fret board but rather slide them to the next chord..its tough but I remember trying to get my muscle memory to do 13 on base and 2 and 4 on snare and hi hat every beat,,that was a huge obastacle to over come but finally after hours of practice it did come.
Im guessing that its going to be the same muscle memory needed to do chord changes,,but I think it will come..right now im practicing a minor to c then g..its hard ..

Allan