Can't find a definitive answer after a quick search but I did dig this up from an Australian Government website.
http://www.crimeprevention.gov.au/In...ime_Module.pdf

The chapter on Motor Vehicle Theft (about compliance plates) in part reads:

"While changing these makes it easier to re-birth cars, it is not an offence
to remove or tamper with compliance plates in most Australian states."

Make of it what you will.

I'm with Gene on this, remove them to paint and restore should be fine so long as they are 100% going back on the same original body/shell.