Originally Posted by ParamountScapin
Problem will be that you are using 10 gears where 9 used to fit. So you will have to adjust your rear derailleur so can only shift through the nine gears you want. You get to pick, though. Either drop out the first or the tenth and set the stops accordingly.
Well, the real problem here is that 9 speed shifters are not about to shift a 10 speed cassette anyway. 10 speed cog spacing is 4.12m and 9 is 4.55mm.