It depends. If you actually fulfil your duty of disclosure (a lot of people dont) and the insurer accepts the risk at the time of inception, then you will be covered for the mods providing they're still within their underwriting guidelines. If you dont tell them about the mods, however, and they assess it they may then deny your claim and cancel your insurance without being questioned, or just cover a portion of the damages. I work for an insurance company (not saying which one just for privacy, etc.), and the number of dickheads we get bitching about not being paid for a claim, even though they didnt tell us about half the crap on the car, is unbelievable!