If a Russian citizen has been issued with a Part-FCL licence but the person has not picked the licence up from the licensing authority yet, is it allowed to hand over the licence?
Yes, provided that the purpose of the license is to operate a non-Russian aircraft, i.e. if the person is e.g. destined to fly as an employee on an EU airline. If the intention is to fly in Russia or Russian controlled/registered aircraft, then handing over the licence would be support to the use of banned aircraft or operators and hence prohibited. For private pilots (who presumably would be flying themselves and are Russian citizens) the license should not be handed over.