Hi Jochen
Yes you can.
In the early days of 50ppm diesel there were some lubrication issue resulting in injector pump failures in diesel engines (talking in general - I have not specifically heard of any issues even back then with om352 engines). These issues have been addressed by the fuel companies long ago so no longer an issue.
Personnally I dont see much sense in using 50ppm though. It costs more and with the short oil change intervals on the OM352 theres no real benefit.
If you however stop at a garage where they only have 50ppm you can fill up without worry...