Thanks remdk, this is very helpful. In which section of the Terms and conditions did you see the info on re-crediting Qcredits? I checked the Qcredits section and it says the following
Qcredits are awarded only to members in certain membership tiers and can be redeemed for various awards on Qatar Airways. Unless otherwise indicated, Qcredits are valid for a period of twelve (12) months and will expire automatically on the first anniversary of the date on which they were credited to your account.
My main concern is whether I would be able to make changes to a ticket upgraded with Qcredits after the expiration date of those Qcredits.
Thanks