AFAIK that's never been borne out by a trial.

The driver is always responsible for the car regardless so in reality I don't see it being an important point. Yes if something fails and it causes an accident you are on the hook if you had modified that system or failed to maintain it properly. The onus would always be on the driver to prove the manufacturer was negligent if they believe the car was not manufactured properly or designed safely.

So I wouldn't mess around with self driving (personally I'd never even use it from the factory) but there's little risk in touching many other things, these systems are designed to compartmentalize and fail safe even when you tinker with them. Though maybe not in Teslas case because they mistake the tribal knowledge of over 100years of automotive design and manufacturing for inefficiency. but I do not know a whole lot about Tesla computer systems, in ICE cars I mostly only touch the engine controls, and maybe traction control. In my current car I suppose you could do some real fucky things with electric power steering and brake by wire.

Most tuners won't go beyond messing with throttle curves and traction control when it comes to anything safety related, as neither would cause any kind of serious failure unless you tried to re write the code to do something it wasn't meant to to begin with.