I agree...a hacking will occur. But when you have issues, and bring the car to the garage...once hooked up, they will find the hack code, and then tell you the warranty is busted. Then what?
This is driven to anticipate you will hack, and they will dump you for repairs early on.
You pays your dollar, you takes your chance...............
You sell a device that SETS the value to on. And can also REMOVE any signs that it was ever there. Then, the user simply “unsets” things before taking them to the dealer, and no one’s the wiser.