I think somebody has done this a long time ago (blasterfreek?) but I haven't seen one cut up. Yeah, do it! Lots of people on here who haven't seen one would probably like to see how Yamaha does the baffling in there.
But if I understand your question correctly, are you going to try to cut it open, 'gut' it, and weld it back together to try to get more power?!
Anything's possible, but I'll be the first to opinionate that that's a waste of time. You won't see much (if any) gain in power. You can find a good used FMF exhaust on ebay for a touch over $ 100.00 if you do some looking.