International flight regulations are strict and that since foundation of ICAO. No, as long as you do not have your physical license in hands, you are not allowed to fly.
It is always the same discussion on exam as well and everybody knows the problem. You are allowed to give your student flight authorization to fly to a remote airfield for examination, but the moment the examiner declared him pilot, the student is grounded until he receives the license physically. You can cry, you can howl to the moon, believe in the strangeness of this, but it is fact and known since a long time.
In all international flight regulations you are promoted pilot by the declaration of the examiner, independent of the paper of a license. If you are a pilot, you have to carry your license. If you don't, you can't fly. It has a reason this has been settled like this and you are not the one to change this part of the world.
I always thought that it is a real bad habit to start the career as a pilot with the illegal solo flight back home after exam on flight authorization of your former trainer. When I did my exam I received a flight authorization from the examiner, which I did not question, but it felt a little less illegal compared to the authorization from the ATO.