There's no consensus on the relative value of APs to HVs. There's some value, but I'm skeptical that it's as simple as "60 APs = 1 HV". In any case, you certainly can move around APs to unlock other guys. I do that often. Anecdotally, I've noticed that a precipitous drop in AP can attract sims, so I try not to drop it by more than ~45% in a cycle. I don't have any data to support it, it's just what I do.