> If I must give one access because it needs a firmware update to fix a bug or something, I temporarily set my guest wifi network's password to something random, configure the TV to use that, apply the fix, then reset the guest wifi password back to the old value.

I use USB based updating for the TV to avoid ever having to give it Internet access. Since it's never connected to the Internet I don't need to care much if it's running the latest version or not, for all I care it could be running the same version until it stops working as long as the current version is good enough.