Charge - the 200 uses a 35mm carb, the 220 a 33mm carb. I know the carb on the NZ & US models differ (how, I don't know, but that came from my dealer).
When you take into account the $ conversion & postage, it's probably around the same price for the pipe (and less hassle).
Jetting: no idea, what area are you riding in, & what altitude?
Restrictors I think are only in the earlier model KDX's, or at least in the SR (street legal with metal tanks), not the "normal" ones.
Putting an aftermarket pipe & muffler on makes a huge difference. Definitely a "must have" mod.
Hope that helps some & have fun :)