as the title says will a 04 STI trink fix to a 02 WRX trunk ?

 

"yes"

but the STi spoiler weighes more so you need to swap out the torsen bars too.

 

you dont HAVE to swap the bars/spring things, its fine without it, im rockin the STi trunk on my wrx, when you pop the trunk though it doesnt open, you have to open it all the way manuallyby grabbing onto the wing or sliding your fingers in the crack where the rear bumper and trunk meet