Originally Posted by
choco14
I will depart from HKG. I wanna put Japan into my itinerary. Do I need to put it immediately after my departure or immediately before I go back to HKG? If my last continent before returning home is Australia (let's say CAI or SYD), can I make use of the transit chance to stay in HKG for one night or so? I wanna unload all my packages before going to Tokyo and Hokkaido..

As others have posted, no.
What you could do is go (using the SWP example), say SYD-SIN. Stop there with a return SIN-HKG-SIN on a separate ticket, then use JAL to go SIN-NRT before returning to HKG.
The hop from SIN-HKG and back in coach can be quite inexpensive. e.g. On UA for about SGD590.