Change Apple ID region and save media library

Changing country entails canceling the first service, in which case deep down in the legal documents: Legal - Apple Media Services - Apple you will find, "When your Paid Subscription to any Service ends, you will lose access to any functionality or Content of that Service that requires a Paid Subscription."

That means you lose any feature associated with the old account.

I faced a similar problem with the exception that I changed the region only for myself, and it changed for all family members with the loss of all music. And here on Reddit they say that this is inevitable.

https://www.reddit.com/r/apple/comments/angn8s/psa_changing_country_in_apple_music_completely/

I don't know. )

Waiting for the answer here: Loss of the Whole family's Music Library … - Apple Community

Yes, but to the extent that all of your playlists won't appear again. You will be starting afresh.