Depends on how heavily things are locked down, and how much money this tech-savvy person is willing to risk on a bricked automobile.

The vehicle comes from the factory connected to the internet.

You'd have to find the exploit before they do, and it would be hard to replicate because once they find out, the only cars vulnerable to your exploit are ones manufactured before the patch who have been disconnected from the internet (which is like 2 cars).

It's theoretically possible but very hard to replicate. And on top of that theres always the risk of the car manufacturer voiding the warranty on your $50k vehicle and/or cozying up to your insurance company and convincing them any damage is a result of you preventing their systems from running as intended.

It's a messy high risk low reward game to play. Better option is to just buy a different car if you can.

Right, but that requires somebody to find and document exploitable firmware revisions, create and distribute hardware/software to exploit them, develop the aftermarket software/hardware, and all that potentially separately for each car model. And then that just becomes a war with the manufacturers, who might try to update their firmware more aggressively, lock things down more, and threaten/sue people working on such things.