Very most likely, it will be separate, as QF5 is (if you do as you plan to), its an orange sticker dom pax on int flight.
I dont think QF will sell you a tix as you plan to do, probably wont work.
You are also having to DIY the bags from dom at T4 to T1 for the CX flight...
Good luck if they can help, but I can only it as a no.
Can only see the bad or horrible that can come out of this odyssey, even if you have 4.5 hrs.
IF you were doing a QFd to QFi, and can a BP and all, and show passport to QFd staff only once, and dont have to go to the counter again (CX or QFi), it might work.
But you must remember, your QF5 is not really an int flight, in your case.
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If you are seriously thinking about 3 bags, do SYD direct to HKG this trip, or even go via BNE or MEL, as its QFd to QFi, and you only have to show passport once to QF staff, who will then issue a QF082 BP for the whole trip.
Going QF5 then CX via PER will only be problematic.
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Personally, I wouldnt dare do it.
Or if I did, I would just do it SYD -> PER as a solo, as a try, and not do a transit to T1.
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Also, as you do QF5 and have not paid the PMC on that sector, it wont be as an int pax.