Had long conversation regarding holes in helmets ST I tend to be with you on that front.
But saying that there were retro fit of Hanss devices on motor sport helmets, The RAC said as long as an authorised person did it it was ok! the problem there was the product you were drilling holes in was a British Standard tested item, tested without holes my contention was once modified it no longer had that approval wither the person who drilled was aproved or not.
I would expect the insurers to be looking at ANY modification of the main structure