I'm not sure I understand how one trains to be part of a culture. You either are or you aren't; you can be born into it or become assimilated as a natural course of life. Specializations are meant as things you're trained for, things you have to go to school for, not the intricacies of being part of a culture. You can't purchase that.
If a player wants to be Correllian, then she can choose the Correllian sub-division1 of Humans -- she doesn't need to have been born on Correllia, just lived most of her life there. Similarly, if someone wants to be born on Correllia but not have the cultural background, he can just use the basic Human template and say he moved away when he was young, or else spent more of his life elsewhere.
1 I was going to call it a "sub-race," but that didn't sound right.