Change iTunes Store country and keep Apple Music library?
In theory if you have a friend who has an iphone and apple music and you both upgrade to iOS 11 then you can follow each other’s apple music playlists then get your friend to save and add your songs and playlists to their device, then on your device switch over app store countries, re subscribe to apple music in the new country and then do the reverse and follow your friends playlists and re add them back to your apple music library.