Dare I say it, but potentially even worse if you need to claim, this could be an undeclared modification too far it it is not as registered or type approved.
No modifications should go undeclared; you should declare them all to your insurer so they can decide if it's something that affects the insurance risk. There'll be a condition in the insurance policy requiring customers to do this.
As you've said, this could count against anyone with undeclared mods in the event of a claim, and would also probably affect any future application for insurance cover.
