In my experience racing rc cars and trucks I learned a bit about tuned pipes. The length of the manifold (the length of pipe between motor and the "can" muffler) makes all the difference in the world. Longer = top end, shorter = low end power.
USUALLY, the designer of a muffler has a typical power range that they're looking to acheive at certain rpm's. A TUNED PIPE is when the length is set for a particular purpose.
So the real question is: what do you want to CHANGE in the performance? That will also help you determine "what" to do. It takes experimenting, and you have to be careful not to cut the pipe too short or lengthen it too long, where you will be moving the powerband to the wrong place.
Personally, I'm quite surprised nobody has really jumped on this to come up with their own brand of pipe...I do know that Dax has one, but I haven't seen it in stock ever.
I also think that if you're looking for a sound change, and perhaps more power, too, that you can remove the baffle from the stock pipe. I've read threads on how to do this before. If you're going to do that, I'd love to hear the results of it. I think that's the quickest and best change you should make because it's not permanant.
I have successfully pulled the baffles out of 2-stroke pipe and gained a performance increase (as well as a sound increase).
Hope that helped!