Sorry mate, I just realised I sounded like a complete cockfag saying that.
I have looked into this quite a bit. You can legally modify your car. Not all mods are illegal, they just need to be done within the guidelines. Included in these guidelines are items that require an authorised RTA signatory (or engineer as they are commonly known) to sign off and agree that they are safe & sound.
The main problem is, the police that defect people don't know enough about the guidelines. Therefore they defect you on the basis that they suspect illegal modifications when in all reality they dont know what is legal or not (to an extent). Then you must clear that defect by proving that it is within the guidelines by getting a pink or blueslip from an approved mechanic or repairing/replacing the item to a legal state.
So, my suggestion is, have an up-to-date copy of the guidelines with you that apply to your mods (assuming you comply with them) and if you get harrased by cops trying to defect you, in a nice way show them that you are totally within your rights to go as far as you have with the mods.
Simple.
Two outcomes from that situation would be you get let off, with no hassles. Or if your a knob, they give you a defect anyway and you have to go clear it anyway.
edit: spelling