Problem is George.. Customer service and claims are two different departments. Somewhere in your contract will be a clause regarding modifications, thats what I would be sticking to.. forget what customer service tells you on the phone, when it comes time to claim.. they hide behind the contract to the last letter. For example they might argue that although it was listed on your policy it has been later found to NOT comply to ADR's as listed in the insurance policy.
IMO they would still have to prove the mods caused the accident.. you could always argue against it, might get messy though.