It was years ago mind, but back when I was into my showing days, I had a fully modified Megane. Not a panel was standard! De-handled, smoothed boot, and bonnet etc. Changed pretty much everything.
I was with Direct Line, and declared everything. When I had an accident, they let me use my bodyshop to put it back to how it was. Some insurers put your price up because it's modified, and then when you have an accident they put it back to standard, meaning you have to pay for the modification again!
Just check, whoever you use, they replace the mods.