You'd be surprised. Don't forget the RX7 owner Vs Highway Insurance story where the invalidated his policy because they found posts on a forum about racing at Santa Pod and a T-Piece in the fuel line, which they claimed was from a previously fitted Nitrous kit.
Plus Direct Line kicked up a massive stink for me when I changed one set of standard fit Toyota Celica wheels for another set of standard fit Toyota Celica wheels!
Plus, increasingly these days it's not the insurance company that check your car over, it's the mechanics at the garage the car is sent to for repair. They will report back and if necessary, the insurance company will send somebody out to validate the garages report.
THis is because insurers are nuptie snot underwriters anymore. Don't know of either case however from brief details.
RX7 if there was no nitro fitted when it had it's bump/used on the road, no increase in risk therefore can't through the case out.
Re the wheels, i have done the same on my elise, again they try and charge more, I ask why, premium based on risk, why has the risk increased etc, They can not answer and do not charge extra premium (after complaining).
Final point, never let an approved repairer anywhere near your car !!!!!