It's not going to happen. A victory by the Japanese definition was to 1] get resources, which are found in the Dutch East Indies, and 2] be allowed to continue fighting China without an embargo. Neither of these requires an invasion of Australia. This sort of victory is *barely* possible if Japan gets absurd amounts of luck (ie. knocks out the fuel storage at Pearl Harbour, and emerges virtually unscathed at both Coral Sea and Midway, while the US has a lot of bad luck especially with carriers), and then the USA does bend because Japan offers lenient terms (ie. withdraw to their pre-1941 borders in the Pacific but scrap the embargo). That in itself is unlikely, stretching it any further is just going to make the USA more angry/desperate depending on the exact scenario.
Then there's the question of just how Japan gets enough stuff together to invade Australia. I think the numbers for the various operations in 1941 (Malaya, Guam, Philippines, whatever else there was) added together to form like 11 divisions. Gather all those men together, and you have nothing more than 1.5 times the size of the day 1 landings on D-Day. But that's your maximum force. Manchuria and China couldn't be stripped of any more forces. I don't know the full size of the Aussie Army, but I doubt it is much smaller than 11 divisions. To say nothing of the inevitable, massive US reinforcements in an invasion scenario.
Then there's supply issues. Guadalcanal was a nightmare for Japan to supply, Brisbane is about the same distance from Tokyo as that, Sydney and Melbourne are another couple of thousand kms. Good luck protecting a route that long from US subs.
But for the sake of argument, let's say an ASB comes along and drowns the entire US fleet and Japan gets given so much stuff that they can pull this off, now what?
The position of the Aboriginals will not change drastically. They don't have the population to. The numbers of them were always in the low hundreds of thousands IIRC, the total (nearly all white) Australian population at this time is on the order of 7-8 mil. The Japanese don't have the resources to massacre 8 million people, so the whites will rule the roost. Any attempt to change that will likely spark a revolt.
Chinese people aren't white, they were massacred. Korean people aren't white, they were treated like slaves. The Japanese Empire was always about Japanese superiority over anyone they could find, nothing more and nothing less.
- BNC