I don't know much, but I did do the MOD. The way it was explained to me was, if you change your air filter you'll get more AIR in. Messing with the carb gets more FUEL in. Drilling the muffler gets more exhaust OUT. From Whizzers to Tomos mopeds, most owners of small engine bikes do the same mod to get more throughput.
At idle and low revs my bike's noise is the same as before the mod. When I gun the throttle, I admit the muffler does not muffle the way it used to. As for the emissions part, if my bike is still alive when I have to do my next test 8O I have no problem buying a new muffler to use for the day.
N2r 150 Xingyue