Welcome
The K&N filter has been added by previous owner, PPP didn't change the filter at all. What do you mean by intercooler pipes have been changed, just the hose between the turbo and ic? If so, I didn't think the hawkeye wrx PPP kit included this, think it was only earlier cars?
In terms of upping the power, then its time for a decat (or sports cat to stay MOT friendly) and remap. Don't push the 2.5 too far though, they're not the strongest engine ever made
