There shouldn't be any problems. You will however need to verify the clamp diameter for the front derailleur unless of course you have a special clamp due to the carbon tubes. You will also need to know if it's a top swing or bottom swing and top pull or bottom pull. As a mechanic for many years, I still can't tell you which is which without looking it up to verify.
Running a triple will require a longer bottom bracket.
Oh, the most important potential problem I can imagine is the spacing of the rear end. 9 speed hubs now require 130mm spacing. If your frame is an older 7 speed it may not work and could cause a potential for damage trying to force a 130mm hub into the frame!
L8R
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