As far as I know, there is no requirement for interstate cars to go through Regency. I definitely had the option of Sturt. My car passed and it certainly isn't stock. It was almost defected for 35% tints, but I managed to talk my way to a 'formal caution', whatever that is.
At the end of the day, Sturt only care about your VIN, engine number and compliance plate. My 97db exhaust was even ignored (and the inspections are carried out in a tin shed). They also looked past other obvious defects including my turbo timer, A-pillar guage, etc.
What's more, I actually received a couple of compliments on the car.