From what I understand, the 9-speed (and perhaps even the 8-speed) derailleurs have plenty of "reach" to work with an otherwise 10-speed setup. Of course, you'll need to set the limit screws and perform the normal derailleur adjustment after the swap but that's something you'd need to do anyway. I'm pretty sure the jockey cogs on the 9-speed derailleur can handle the narrower 10-speed chain without any problems. Good luck!