Thats why i said "Almost". It all depends on the available fare classes on the day of change. Expect to pay more for the flight you want to change to if that flight does not have the fare class of the original booking.
However, I find if I ask nicely at the lounge with my boarding pass in hand I sometimes get a "fly ahead" using a discounted advance purchase J class fare.
What we should not do then is expect we will also get it next and every time we ask...And don't then think QF has inconsistent service if we don't get it - That we don't get it everytime when it's effectively a gift is not inconsistency.
Here is the domestic business fare condition:
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