Moving vast distances and keeping app store purchases
First: keep your apple-id in one “Country Store”. Don’t change the country of your apple-id. Apple will screw it up, throw away your purchases or something of the kind. You can move an apple-id to a new country store (and back again), but it seems like an afterthought from Apple. You will only be able to see/access your purchases from the country store presently associated with the account.  

Stick with what you have for the moment. If you really need a new apple-id / iTunes account in the USA; Make a new one. Your old apple-id and purchases can live alongside the new on the new i-device and in the same iTunes library.