Our laws are State based. You pretty much get free reign in Tasmania and in the Australian Capital Territory (Canberra) which sits inside New South Wales where it’s much more strict along with Victoria, South Australia, WA, and Queensland.
The rule is 130kW per tonne so does include modified cars....You’d have to get someone else local to me with experience of registering modified cars to respond knowledgeably. All I know is police have a habit of defecting highly modified cars usually on the pretext of safety.
We need something like that here, can you not get the car remapped so that it complies with the legislation. I know mapping is normally used to increase power so must be able to be done the other way