Don't bother changing them over. Most of the new rotors come with races installed. The odds of "dinking" up the old races are pretty high because you need to drive them out using a punch and hammer.

Buy some new bearings and be done with it. If the new rotors don't have the races then install them using a race driver. If you don't have one and don't want to buy another tool (yeah, right!) then swing them by any mechanic shop and they'll install them for you.