I did that back in 2006 using a dremel with a grinding tip. I spent a long time checking and rechecking that all teeth make good contact. My kickstart has worked flawlessly ever since, the only cost was the gasket. I have one of those magnifying lamps that helped see closely the teeth and thier contact pattern.
My bikes getting old, it's a 2004, but I still think it's the best bang for the buck. I still run into riders who think thier new 450 four stroke is the fastest bike in the world, then the old KX has to spank em, next comes thier excuses. You all know what I am talking about.
John