In general you can only enter each of the the three IATA zones once. They are:
1: Americas
2: EMEA
3: Asia & SWP
so you cannot do what you suggest because HKG is in the same zone as SYD. SYD-HKG-JNB-LHR-JFK-SCL-SYD is fine, as is SYD-JNB-LHR-SCL(transit NA)-JFK-HKG-SYD.