I've received a reply from the developers. The following steps turns off "steam cloud" so after you uninstall / reinstall you are able to input a different email.
If you ever get stuck in the "logging in..." loop while trying to log in with Xbox Live (steam version) try this
1. While the game is installed, Right Click > Properties > Updates > Uncheck 'Steam Cloud'
2. Uninstall the game.
3. Steam > Settings > Cloud > Uncheck 'Steam Cloud'
4. Open File Explorer > Navigate to C:\Users\UserName\AppData\Local
5. Delete the entire folder entitled 'Maine' (if a cache file can't be deleted, that's okay.)
6. Re-install and start the game.