Yes, it is possible and if there is availability, easily done. The complication arises potentially when using QCredits on the return if the system rejects your GGK-DOH-CDG upgrade (which presumably costs 40 QCredits). If you are then forced to do it at the airport, where they will only allow upgrades one leg at a time, you will not be able to do a 40 Qcredit upgrade all the way to Paris. Any split upgrade would almost surely leave you with an insufficient number of Qcredits to upgrade any remaining medium haul leg (e.g. DOH-CDG). So you have to plan with that contingency in mind. On your last question, even if you renew Gold by April, the new QCredits are only added in July as the cycle runs 12 months. Sadly, say if you are left with 15 Qcredits from the trip back that you are unable to use, it would not be added to the 40 that you would get in July. Those would expire that day and you would start with 40 in the new Gold cycle.