Premium lapsed a couple of years ago as I'm happy with basic info as I'm playing very little golf due to illness issues and using the Rapsodo as a practice motivation in my back yard oh well another hurdle to get over...
If you were to sell it that new person would have to create their own account and pay for the premium membership.
I can't say one way or another about changing email, but it would be your premium account that is attached to the email. Which makes sense. Best thing you could look at when your membership is up, stop and start it up with a new email address.
To say myself, as well as the entire mod staff, is excited for this opportunity for the forum is a massive understatement. Huge thanks needs to go to Flightscope as well for going ALL-IN with us on this test and @GolfSpy_APH closing the deal on a great call with them. I have a feeling it could lead to a great relationship with FS going forward as well!