here is a post i found trawling the internet off the RX8 forum :-----
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Here in Victoria mods are quite restricted.

Below is my understanding (check first as I have been wrong before).

1. Changing/adding forced inductions - Changing I believe you are allowed one mod to the intake, but all plumbing must remain stock. Adding FI I think will kill emissions and therefore be unroadworthy. Any serious hp mod will require an engineers cert

2. Running with/without a catalytic convertor (emissions) - Thats a no no.

3. suspension, shocks, springs, coilovers, sway bars, end links etc...any height restrictions - Springs/shocks are free for all. Minimum height of any part of the car is 100mm. They have a 100mm cube and pass it under the car. If it hits anything you fail

4. Exhaust (sound/size restrictions?) - There is a noise level. Don't know what is is

5. ECU modifications - None, under any circumstances.

6. Brakes - Apart from pads and fluid an engineers cert is required.

7. Body kits (including widebody and cutting of stock fenders) - Not sure. I think go for it

8. tire/wheel change restrictions! - 25mm increase in wheel size in either direction

Then I've read about getting engineering certificates and things of the sort, what is the difficulty in getting one of those? - Vicroads has a list of automotive engineers. Go visit one an he will check your mods and if he approves you get a certificate (for a cost of course). From my understanding they are generally quite reasonable to deal with.

I hope I'm not asking too much! - Not yet

Thanks! - Is ok

In reality most people just go for it. If your car does not stand out too much and you don't drive like a dick you are generally ok.

Hope this helps

Matt