fair enough, things are often misinterpreted on car club forums, it is wise to point out in this case that running with an undeclared exhaust potentially means running with a void insurance policy.
The only advice to give in this case would be to cancel and insure with a modification friendly insurer.
Just depends on the cancellation policy in place, not worth cancelling if its going to cost you. Just keep saving the money and then put a few mods on when your policy expires and move to another insurer that allows mods, try Sky Insurance!!