I've heard that, once you remove the plug, the pellets can be taken out, then there is a baffle under the plug that can be reached with a air chisel, or cutting torch to punch a hole through it to allow better flow. That baffle is used to redirect exhaust flow. Then you need to straighten the plug out, and weld it back in to the body. It looks legal, but nothing in there to obstruct flow.
I've heard this, never have done it, of course, because of the legal ramifications....
