I suggest not adding an access port or downpipe.
If you're in the same boat as most average people who didn't win the lottery or have rich daddy buy their car; spending 30k on a car is a serious chunk of change. I'm assuming you'd like that warranty which protects any issues of your recent 30k investment, to be intact.
Adding an access port or downpipe or both, is the fastest way to absolutely void that 5 year 60,000 cover your ass(CYA) warranty that was included with your new WRX on the most expensive parts of your vehicle(engine/transmission). The easiest way to protect that warranty is to add the SPT performance parts, or purchase parts that are easy to replace quickly AND without signs of being tampered with. I got about 600 miles on my WRB WRX hatch and the only mod I'm doing is an axle back because the SPT exhaust just doesn't deliver the note of the song I want my outback choir to sing from my Subaru. I can remove the axle back, spray paint a silver coating on the original bolts to show no signs of wear, and reinstall the stock muffler in less than half an hour.
Yeah, I got this figured out.