For my first question, the answer is yes. I’m just tired.

Just setup security to enabling demo users. then create a user with admin role in prod

Disable security and repubish.

For the second question, it seems it is not possible for Free apps to restor backup.

Restore a Backup - Developer Portal Guide | Mendix Documentation

I could perhaps use the replication database module, but too many efforts for me. I shouldn’t have cleaned the data on my local environment :)