Very true, but in the unlikely and unfortunate that you are are involved in a crash resulting serious injury (or worse), even if it is not your fault, EVERYTHING about all vehicles involved could be called into question. In that scenario having your claim rejected could be the least of your worries.
Not to be appearing dodgy, but I really don't think anyone could tell that the rails have been modified once the seats are in. Also, unless they completely break up for some reason I don't see how insurance could try and void my claim for it. Anyway, this is something that I'll get Lurch or someone alike to fab up for me so I am 100% sure that it's up to and exceeding spec.
Don't want to seem like a kill joy or stick in the mud, but seats and seat belts are serious.
Just my opinion