If this were me I would ticket it on paper with the HKG-SYD as OPEN. Then confirm on the QF flight and waitlist for the CX flight.

Also Expertflyer is telling me that CX161 (departs 21:25, i.e. 2h20m later than CX111) has D9 availability every day in January, so if you confirm and ticket on that I don't think you'll need any sort of reissue to move to CX11 later if that becomes available.