If you are in one of the 22 counties that require emissions inspection, this is what the emissions inspection consists of:
Since all the emissions parts on the Fiesta ST are from the catalytic convertor downpipe and upstream, the catback exhaust doesn't matter from an emissions standpoint. The OBD inspection would be looking for emissions related codes like P0420 or O2 sensor codes, MAF sensor codes, etc.
The safety inspection, required in all counties says this:
So you'd have to have an exhaust system of the same type as OEM, i.e. pipe from cat, exiting at rear of car, containing muffler(s) without cutout devices.