I see that there are a lot of litigation experts. Such an easy out... blame them darn lawyers dangnabit.
For those of you so scared of being sued 3 owners later, you have a lot more to worry about than just the ROPS modification. If an accident was truly litigated the attorneys would crawl over every inch of the tractor for the slightest modification that was made elsewhere to deflect from the ROPS issue. But lets be realistic --- you won't be sued.
They would go back to manufacturer anyway for the deep pockets, and your modification may get the manufacturer off the hook, but it would die there. A tractor owner is not an engineer nor manufacturer so there is no expectation he knows what he is doing, and therefore he cannot be liable. Since there is no law against this he can't be pursued that way either.
Plus, a lawsuit like this would be taken on a contingency basis by an attorney, he is not going to risk working for free to come after an individual.
MikePA , why would you post just to say you don't know?