From my personal experience, I have only heard of one person "crossrating" into nuke. He was a prior nuke that got dropped from the program, did well as a conventional out in the fleet and got accepted to try again. I have never heard of any "air" rate being crossrated for nuke. But yes, we do get liberties in phases, usually after A school you have the most liberties, with the exception of living out in town. That happens in prototype. But keep us posted if you are trying to crossrate, I'm sure alot of people would like to hear how you did it, if you can get it done.