This is not exactly uncertain ground. Car manufacturers don't have liability when their customers modify their cars. Whoever made my clothes dryer doesn't have liability for any unsafe condition I may or may not have created when I removed that stupid annoying buzzer.

Yes, for exactly the same reason that if I overclock my intel CPU then if it starts a fire intel won't be blamed because they expressly put that if I overclock or modify the CPU settings from the factory default they wont be liable into the terms of service and unlike many software SLAs it is accepted by courts around the world

Of course they will. If a hit man cuts your brake lines, Ford will not be liable.

I absolutely think JD would escape liability. Consider the more egregious cases of any number of high-profile companies who have had significant customer data breaches in recent memory. Regardless of how negligent they may have been (lets say they stored user passwords in plain text), have you ever heard of a company being held responsible for even the most egregious/reckless behavior?

Independent mechanics have been repairing machinery for as long as machinery has existed. This is not an exotic legal problem.

Life is full of risks. This is, or may be, one of them. Allowing a handful of opaque corporations to monopolize the tools of food production and dictate their after-sale use is another risk.