I've modified my Speedmaster pipes. No photos I'm afraid. Being a cheapskate I decided to do it with the tools I had to hand. Here's what I did:
1 - Drilled a series of 5mm holes as close together as possible around the end of the exhaust (in the black bit between the tube and the outside of the exhaust).
2 - Hit an old screwdriver with a lumphammer to pierce the metal (the black bit) and connect the series of 5mm holes together.
3 - Insert the old screwdriver down the "slit" I'd created in the black bit and hit it with the lumphammer until the plate the driver is pushing against is pierced. The plate is approx 8" inside the exhaust. Gradually work round in a circle until the plate is pierced all the way round.
4 - Pull the inner tube out of the exhaust. It should come out with part of the inner plate attached to it.
5 - Use a small grinding wheel attached to the end of a drill to grind the inside of the exhause exit smooth.
It worked for me, honest
I've got a few minor scratches around the inside end of the exhaust, but nothing that you'd spot unless you were looking for it. The result is an exhaust that sounds just right IMO. Not too noisy, but a bit throatier than standard.
I bought a secondhand set of standard pipes as insurance before I did it.
If I was doing it again I think I'd use 2 hole drills on the black bit - one just big enough to go around the exit tube, and the second one almost the full diameter of the inside of the pipe. That would leave you a nice neat circle to work in when removing the inner plate, and should mean less chance of scratches.
I'm looking out for another cheap set of standard pipes to test my theory
