The inability to issue your BP in the past had nothing to do with the need to clear customs. Domestic sector BP's are routinely issued at foreign ports by both QF and other airlines, providing the flight is open for checkin at the time.

And note that issuing a BP and checking luggage to a final destination are not linked. Though in the case noted, you need to collect the luggage at the final Australian international terminal in order to clear customs. But it may still be tagged to the final domestic destination which can save time at re-checking.

Since you will need to re-check you luggage after clearing customs, there is no real benefit in having the BP issued in AKL. You will still need to collect you luggage and re-check it in MEL, and if you miss the checkin deadline having a BP in your possession is not going to help. In fact, you may be better off not being checked in and explaining to the MEL agent that your inbound QF flight was late and they may just move you to another QF flight or may permit you to pay the standard change fee and upgrade to an available fare per the terms of the fare you purchased. But if you have the BP issued in AKL, you may be considered a no-show at boarding and lose the fare altogether.