Can you convert a Yamaha tw200 to a kick start?

Yes, the easiest path is to use a 225 conversion kit, part number 3RW-W0795-00, and get an early TW200 kick start lever (the kit unit will not fit). See the many threads at tw200forum.com for more info on this. Costs are reported anywhere from $150 to $450 depending on where the parts are bought and who does the labor.