score:6
The reason to enter your Global Entry PASSID in the airline's booking system would be so that you can qualify for TSA PreCheck when you depart from the US, with expedited security screening (no taking off your shoes, etc). Your PreCheck status has to be shown on your boarding pass (having the Global Entry card itself does not help). However, Qantas is not a participating airline in TSA PreCheck, so in this case you can't do that. You will have to go through regular screening as you depart from Dallas.
When you return to the US, after getting off the plane, you can use your passport (not your Global Entry card!) at the Global Entry kiosk for expedited immigration processing. This does not require any sort of advance registration with the airline, as far as I know.
So, short answer: there is nothing you can or should do with your Global Entry number, or your card, on this trip.
Also note that Global Entry and TSA PreCheck are entirely unrelated to redress numbers, except that some booking systems let you enter the numbers in the same place. Redress numbers are meant for people who, for instance, have been mistakenly put on no-fly lists because they have a similar name to a suspected terrorist.