No, don't do that. You'll probably render the card unusable. The TSOP memory on the 9600NP won't run at Pro speeds. Far from it in fact - the most you can realistically expect is about 250MHz. I doubt volt-modding will help either.
You can't use ATi Catalysts later than 3.4 if you want to overclock the card, so use the latest Omega drivers and RadLinker:
You can expect 400MHz+ core speed and some nice performance increases, but getting close to 500MHz (as the Pros can) is tricky since the stock heatsink is glued to the core and I'd think twice before prizing it off!