If you keep the same Apple IDs and change regions, you should retain all your purchases made in the first region (USA). You won't be able to update them when you switch regions unless the new region has the exact same version of the app. You can then make purchases in the new region. As you switch back and forth, you should retain access to all apps and data. The only problem is subscriptions. Your have to cancel them when switching regions.
You can use two different Apple IDs, one for each region. Apps will still work when you switch regions. Whether you want to use one Apple ID or two is your choice.
You need a zero account balance and you need to cancel all your subscriptions. If you have cancelled all subscriptions, but some haven’t expired, contact iTunes Support. You need a valid credit card issued by a bank in the country the store is in and you need a billing address in that country. If you have an account balance, either buy something more expensive and pay the balance with a credit card or contact iTunes Support and ask them to zero balance your account.
Purchases - View, change, or cancel your subscriptions.
Purchases - Subscriptions not billed through Apple
Region - Change your iTunes Store, iBooks Store, or App Store country or region.
If necessary, contact iTunes Support. Follow through the screens to get a chat or telephone option.
iTunes Support – world wide
Apple Support schedule phone call
