Well, short answer is no to both. But there may be workarounds.

Do you travel OZ-US often? If so, cancel your current ticket and use it for future travel. Then rebook a new ticket on line, with the discount, and with the promotion.

If you don't travel the route often enough, there may be one other option. How long ago did you book? How far away is the trip? Has there been a significant schedule change? If there has been, you can request a cancelation and refund (though it may not be granted).