Be honest with your insurance company because I was in the same boat a few months ago. I got rear-ended and the axle back section of my Buschur TBE was damaged. The adjuster asked me if the exhaust was aftermaket and I reluctantly said yes. She stated that it was okay and and actually encouraged me to make a list of the parts on my car with an invoice stating the value. The reason for this is that most aftermarket parts are much cheaper than OEM. OEM prices are what our insurance rates are based off of. Once I provided the list to my insurance company they adjusted my premium to reflect the replacement cost of the aftermarket parts. My monthly insurance bill dropped by about 25 dollars. USAA is trying to encourage this to place pressure on the OEM parts producers to lower their replacement prices, thus lowering their insurance operating costs, and finally trickling the savings down to the consumer by being able to offer lower quotes.