I would think that you could use the MAC address of any EV you own that Tesla accepts. However, you couldn't distinguish between the two vehicles in reports on charging, and if Tesla decides to block that MAC address for whatever reason then neither vehicle could charge at Superchargers.
Similarly ...

As I understand it, the powerline communications interface has a MAC address. I assume they're doing MAC address lookup to fingerprint the vehicle. (I think that's how Autocharge works.) I assume each OEM has a separate block of MAC addresses they program into the PLC controller, but I have never ...

Just realized I stopped getting updates from the forum's RSS feed on July 15. I get a 404 error from Nginx on app.php/feed, but it works on port 8443. I had to use port 8443 to log in. Updated my feed reader to use port 8443.