The thing is modifying your car and doing it all "legal" will make it easier to clear a defect.
It will in no way stop you from getting a defect.
Police in NSW can defect you if they believe the vehicle to be un-roadworthy. It can be a dead stock car, and they can defect it.
You can fully legitimate engineer papers and they can defect it.
Police don't have to be able to prove that your vehicle is unroadworthy / doesnt comply with ADR's, they just have to reasonably suspect.
The thing is when they give you a defect, you cannot dispute it. You still have to go and stuff about to get it cleared and rectified.
Best thins is to have a GOOD attitude, that always helps.