I am not in the know, but this is my guess:

scenario 1: before you can resume your owe in MEL you are going to have to re-issue and pay the fee + the additional ticket.

scenario 2: re-issue and pay fee + additional ticket.

scenario 3: your best bet, *if* QF goes for it. QF could, if they wanted to, take your CNS-MEL coupon and give you a CNS-XXX-MEL e-ticket in its place, with no re-issue, no hassles, and, hopefully, no fee; but, the fact that your inbound to CNS is not part of the owe will probably play against you.