There is a exhaust end adjustable baffle called "Super Trapp".
It uses removable plates to add/remove silencing or back pressure. More plates less back pressure more noise...fewer plates more back pressure, less noise...something like that.
SuperTrapp: Performance Exhaust
Have seen Super-Trapp built into a removable exhaust tip...the assembly held in place on the exhaust end with springs...run it on the street, remove it for the track.
Look at MAECO motorsports. They used to sell a removable Super Trapp assembly that would fit into the tapered end of a 427 Cobra side pipe...held in place with a spring or two.
Pete