Hello Alacampagne,
It seems you have questions related to multi-regional device use, and we're happy to help clarify some available options.
It is possible to change the region for your Apple ID by following the steps from Change your Apple ID country or region. To do so you must have a payment method for the new country, as well as a zero Apple ID balance. The benefit of this option is that you will retain access to purchases or subscriptions that are available in both countries. A possible disadvantage is if you frequently travel between these two countries you would have to complete these steps each time and potentially need to redownload content after each change.
Alternatively, you may opt to set up a new Apple ID for use only in the new country. You'll still need a payment method for the country in question, but this would allow you to keep the devices and accounts separate and potentially simplify the process. Purchases for each account would only be accessible on the device that account is configured for.
We hope this helps!