I may be wrong. You aren't changing the first leg, but you are changing the ticketed points.
danger, check with QF on what they say.
Code:
CHANGES BEFORE DEPARTURE
A/ CHANGES ARE PERMITTED PROVIDED TICKETED POINTS
REMAIN THE SAME. IF THE FIRST FLIGHT COUPON IS
BEING CHANGED AND THE FARE LEVEL HAS INCREASED
SINCE THE TICKET ISSUANCE THE DIFFERENCE BETWEEN
THE OLD AND NEW FARE BE CHARGED. IF THE FARE
LEVEL HAS DECREASED SINCE TICKET ISSUANCE NO
REFUND WILL APPLY.
-
B/ CHANGES TO TICKETED POINTS ARE PERMITTED AT A
CHARGE OF USD125.00 PER TRANSACTION. IF THE FARE
LEVEL HAS INCREASED SINCE TICKET ISSUANCE THE
DIFFERENCE BETWEEN THE OLD AND THE NEW FARE WILL
ALSO BE CHARGED. IF THE FARE LEVEL HAS DECREASED
SINCE TICKET ISSUANCE NO REFUND WILL APPLY.