Thanks! I've never thought of this scenario before so glad to know the answer!
That orange stickered BP does not allow you duty free purchases.
Also, be prepared for an terminal and aircraft swap, ie, you have to short notice, go to T3 instead of T1 and get onto a 737.
They (QF) do an equipment swap occasionally.
Years ago, they used to do a lot more of these "domestic passenger on an international flight" scenarios.
You also have to go through international security screening, so give it a bit more time than domestic, as there are a lot more people going through immigration and international security, than domestic at SYD T2 and T3.
I have done it (SYD - MEL) as in your scenario several times.
HLO no LGAs, or only in less than 100ml in clear container etc.
Nice to try that 787, but give it a bit more time on departure, and on arrival.
You also dont get to keep the orange stickered BP, as you will give it to staffed counter, on your arrival into T3 at PER, it will be like you giving your IPC (incoming passenger card) on arrival into Aus.
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At T1, if you do not receive email or sms to go to T3 (equipment swap), go to the T1 QF counter to check in, you wont be able to do OLCI either, as they need to see your document, and issue you a paper BP (with orange sticker).
Then go through outgoing security screening, hands akimbo, stand sideways, legs apart, once clear, get your BP with orange sticker, show the ABF officer, he/she might note it, (not sure if they will still stamps it), as Aus now does not stamp passports, or marks it, then you go to your gate, or if you have lounge access, go there first.
Then to flight.
On arrival at PER, go through to ABF immigration incoming, show your BP, they either mark it or stamp it, and then you go through AQIS DAFF, and then, just before going out into public area, hand in your orange stickerd BP.