Dirty_Idea SYD-CBR-SYD is classed as a domestic not an international flight! So QR cannot issue tickets for those flights. You are out of luck there.
Leaving a flight at a technical stop would be regarded as not completing the flight and result not only in delays to all the CBR passengers but would also almost certainly result in cancellation of the remaining reservation. If you want to visit Sydney then it is at your cost not QRs.