Possible, but I doubt it. The orders for the application of stammkennzeichen, which remained in effect until 1st July 1944, specifically require that the markings be applied in washable paint. Given that the markings were applied at the point of manufacture, prior to any ferry flight, it seems likely that the rules would have been followed. German aircraft factories, just like everyone else's were populated by inspectors whose job it was to make sure that the rules were followed. It was to the RLM inspectors (along with 'aircraft offices and airparks', also replete with RLM officials and only issued here by 'special order') that the codes were issued.
If that is indeed a factory code then where was the photograph taken? The codes were supposed to be removed on delivery of the aircraft to its destination. They applied only for the duration of the transit flight(s) and were to be removed 'without delay'. The unit receiving the aircraft was further required to inform the inspector at the aircraft plant (or at the aircraft office or air park) that the markings had been removed within three days following receipt of the aircraft.
Cheers
Steve