Well, my insurance company does not seem to know about this. I think yours do not want to, may tell you they do not have to, but in the end are required to. There is a huge difference with what some will tell you and what they have to do.They are not required to pay if you purposely modify a ul listed product voiding its listing and making it potentially unsafe. Believe me they don't have to pay in that case i have gone on enough insurance evaluations to say that with absolute certainty.
Every repair of every product potentially nullifies the UL listing, does not mean you can not repair/modify things. Replace the brakes on your car with non factory brakes, change tire types, install a wood stove inside a fireplace, etc. All altered the original design plan, this does not mean it is wrong or unsafe.