Lots of laws, rules, policies, theories being quote. Anyone has links to actual court cases (party A vs party B) where someone with a modded vehicle was found criminally responsible and / or total denial of insurance claim?
It takes a lot of court work, including hiring "expert witnesses", to prove a vehicle's modification is the contributing cause, to the point where an OEM vehicle could've entirely avoided the situation. In a criminal case, you'd have to prove that beyond a reasonable doubt, which is very difficult.
Hypothetical case: say you swerved to avoid a deer in a modified Jeep / LC / F350, rolled, and slid into traffic causing bodily harm. They can't just say "you were modded, thus it was the sole contributing factor". Remember, the defense would also have their lawyers, and expert witnesses if needed. All defense has to prove is: a stock F350, loaded to OEM GVWR, with a high center of gravity, would've also rolled. There's no law against load COG @ legal GVW.
Sure, you'd be at fault no matter what, but to deny your insurance or hold you criminally liable solely due to modifications, would require a LOT of work. Maybe if Bezos or Musk was killed, it would be warranted, but not something you see daily.