making flight changes when prices drop
 

I booked a "cheap" return flight CBR-MEL, but with the current sale the same flights are available for $50 less. It was a red e-deal; can I rebook the old flights or does it need to be a different date (I'm not too fussed about changing dates). If I rebook to a cheaper flight, what happens to the $$ difference?

Try the change flights on the website, you should be able to get a price before committing the change.

It would be better for you to cancel the original booking and rebook it the same flgiht using the orginal fare as credit towards payment of a new fare.
But as per the fare condition, you cannot re-book and travel on the same day.

Besides, you would need to pay $38.5 itinerary change fee for any changes whether it be flights or dates, so the net beneift is very minimal. The $$ differnece can be used as credit for future QF flights within 12 months.

Hope this helps!