Likely yes. Even to fit an STI IC you'll have to upgrade the scoop (because of your model year) and the splitter. There's a thread on NASIOC about what scoop will work for you.
Well you can modify the splitter, but then you still have that tiny '02 scoop. Not sure what the percentage open area of an '02 is vs a JDM STi scoop, but it's likely significant.
The '02 needs a bigger scoop for the stock intercooler according to Subaru's own testing. That's why it got bigger on the next redesign. If you plan on making any use of the larger intercooler, a larger splitter is 100% required as is the larger scoop to accommodate said splitter.