Originally Posted by
vincewy
After the validity period, you may still make changes to the upgraded flight and pay change fee (based on economy fares), if the segment(s) doesn't change.
For example, if you originally had economy ticket YYZ-IST-XXX but with only YYZ-IST upgraded, and you make change and reroute to YYZ-IST-ZZZ, you can carry over your upgrade to YYZ-IST-ZZZ with YYZ-IST upgraded, provided the new flight has J available. You only pay ticket change fee (including repricing of fares), don't need to pay $25 fee for miles/voucher re-deposit, which in this case the voucher would be useless, this is call Upgrade Carryover.
I know this is very confusing and recommend getting this done at ticket office, rather than over the phone where someone can potentially ruin your ticket (ie cancelling your original flight/voucher/miles with no way of recovering it).
See my post here back in June 2017.
Thanks for this info as I was told differently at the local TK office when I tried to make a change to such a ticket (but then they told me already may things that were incorrect).
Also as far as I know, voucher re-deposit doesn't incur a $25 fee as does miles re-deposit. Correct me if I'm wrong.