moving from trz19 membership to a regional stand alone

Do you have to reinstall the new regional and uninstall the original membership version you had - not quite sure how this works

No you don't have to reinstall the game as its the same version regardless how you got it.
If you own the game, and bought it during the subscription, then it should continue to let you in. If it fails to, then you'll have to contact the helpdesk.

Any DLC content you don't own will show up as inactive in content manager, which you can uninstall.

Cheers

thanks - understand it now