I'm thinking given Australia's generally multicultural population, it would be fairly easy for Indonesian soldiers/saboteurs to hide in plain sight just by wearing civilian clothing and keeping their weaponry well hidden. If even just one got hired by a refinery, they could do some serious damage over a period of time just by "accidentally" setting a valve the wrong way, or hitting a switch at the wrong time. Add in a few explosive charges here and there and well....
Even a more overt attack such as a raid on a critical facility (power distribution, generation, etc) could do a lot to cripple the country, or at least the local area, and unless those involved were caught in the act, again it wouldn't be that hard to blend in with the rest of the population, especially if they'd been living in the area for a few months or more.
I started re-reading a book from my collection last night which I probably should have picked up weeks ago - "Australians at War - Modern Military Towards 2000" published in 1989.
https://biblio.co.uk/book/australian...0/d/1032384970 The first chapter which was written by several retired senior Australian officers details a scenario in which raiders keep Australian forces occupied over in WA, while a landing takes place in far north Queensland. The opponent isn't named, but it's fairly clear who they were talking about....
The scenario (both parts) would work very nicely in tying up a large number of Australian troops and ships. A very nice diversion while the main Indonesian force moves into PNG.