Twilight, you have to be careful doing things like that. If he has an accident with a cf bonnet on and it is a front on accident, besides some of the crumple capabilities of the car being lost, insurance can refuse to cover you because you havn't declared the bonnet (it is an illegal modifcation).
Edit: Don't forget they have a person from the insurance company come and look at the vehicle to determine the damage (an assessor). If they see there is an illegal mod, it is entirely up to their discretion whether they cover you or not, from my understanding.