My work with my own clients and those of my colleagues who regularly take on clients in Sydney seem to indicate that no adjustment is necessary for Australia. What works up here appears to work "down under" just fine.
My usual response to clients who talk to me about the southern hemisphere theory: I'll change the way I do it when the luo pan needle points in the opposite direction.
If the earth does not see fit to change the magnetic aspects of qi in the south, I see no reason to think myself smarter.
