So I was doing some pre spring cleaning of my garage and car today and I got to thinking about my plans to do LT/ORY into what I thought was a magnaflow catback that was on my car. However I discovered a reciept in my car which shows my exhaust as a Magnaflow Performance Muffler #12266

My question is do I have to buy a catback when I do my LT/ORY or can I build into this muffler that I have? If I am able to build into this muffler would I be robbing myself of alot of power that I would get if I bought a catback?

Not sure why this woman (previous owner) would have gone this route instead of the catback all she needed to spend was another 100 bucks