Ok as someone who has NPP exhaust and has done the pull let me explain. By pulling the fuse in the trunk it basically doesn't allow the butterfly valve (which is after the muffler) to close after the the car is started. It is defaulted open at engine start. So by pulling the fuse it just keeps it open. The butterfly valves only use is to open at higher RPM's so during normal operation of the vehicle it is quieter running in the car and outside. I personally like the sound of it better with the fuse out. It will no pull any codes or effect normal operation.
1964 Plymouth Barracuda Candy Apple
1962 Ford Thunderbird Baby Blue