If your car is parked on any street in PA and doesn't have a valid inspection it is liable for ticketing/citation. If it's parked on a residential street in the suburbs its less likely to be ticketed unless a nosey neighbor calls the car in. This has happened to me. I'd pack my bike in my car. Then I'd leave my car out in the burbs and train back into town to beat traffic and the horrible parking situation, using my bike to get around from car to train station, and station to home. It worked well for a while. But neighborhood people took notice of what i was doing and started fucking with my car after a while, leaving notes and leaving trash on my car etcetera. Folks do pay attention out in the burbs. Anyway.

Switching counties isn't going to save you from a potential inspection violation ticket. Also your car is registered to your legal address, so if thats philly then its philly.