I had a guy I used to work with bought a new mini. He didn't know much about cars. It had a front splitter fitted which was hardly noticeable. He didn't declare it because he didn't know it wasn't the norm. His has was hit from behind whilst parked at the side of the road. He had to claim as the other drive didn't stop or leave details. The insurance inspected the car and refused to pay out as it was "modified". Thankfully the other driver was caught thanks to CCTV.
Point is that insurance companies are just there to scam. They get away with charging over the top because its a legal requirement. The "modifications" had nothing to do with the crash which just proves they were trying to get out of the claim and all costs.
After that I don't take any chances.