That's really interesting. It must be one of those things that varies from State to State and perhaps council to council.
I just called City of Sydney planning department and they said, among other things (like heritage issues), you can't change the configuration of rooms without council planning approval.
I'm not questioning Austman's information but it does seem strange to me that you could make structural changes to a building without any competent oversight authority's approval.
My advice would be, check with your local council's planning department (or risk an order to reinstate if everything goes pear-shaped).