I remember trying to get a plate for my bike rack in NSW. From memory, even if you take it off your van and put it on your rack then it may be legally too high. (NSW). I also think if you tell them you lost your rear plate, they'll give you a new one straight away, with a different rego number.
NSW make things difficult.
This is why I ended up making a bike rack that fits onto the front draw bar.
Another 5 advantages with having a bike rack on the front are
1. You can always see your bikes in the rear vision mirror as your driving so if anythig gets loose you see it, and fix it before it's too late.
2. No chance of obstructing rego plate.
3. The 2nd plate for rack isn't needed. (Not that you can even get one in NSW)
4. My van (14.44.2) has fold down bed at rear so I don't need to remove bikes to set up.
5. Extra weight at rear of van isn't a concern.
I`m happy with my front mounted triple bike rack. I`ve driven it to the Sunshine Coast and back and had no dramas at all.