Changing App Store region and keeping my purchased items

Chamelo,

There won't be a remnant balance, because it has to be zero before you can make the change. Also, you have to have no active subscriptions, which might include iCloud, I am not sure. For more details, look in here:

Leave Family Sharing - Apple Support

Songs, etc., that you have purchased and downloaded will still work. Make sure to keep a backup, since the ability to re-download purchased items is only in the original country of purchase.