VISITING another state or territory is not an issue. People do it every day. In fact, along the NSW/Queensland, NSW/Victoria and NSW/ACT borders there are people who live in one state and work in another and thus drive interstate all the time.
It's when you change your state/territory of RESIDENCE that you are supposed to change the licence and registration.
However what's supposed to happen doesn't always happen in practice.
Not so long ago I was working in New South Wales with a Queenslander who didn't change his licence or his car's registration, because it was cheaper for him not to do so. He still owned a house in Queensland, but as he'd moved interstate to take up a new job he could have been prosecuted and fined, as he would be deemed to be a New South Wales resident and an unlicensed driver. I think the bottom line is that each state wants to get as much revenue as it can from its own bureaucracy.
As for Kilhal's original question, I think the authorities in South Australia would probably say he's a temporary resident because he's working, and should have a local licence. He should check with them. And because of the nature of Australia it's quite possible that the authorities in one state may have a different view from those in another.
Hope this clarifies rather than confuses the issue.