Thanks Manoj.
In the meantime I also found SAP Note 1988546 which refers to ADAPT01719723. A tentative fix to be included in DS 4.1 SP3 P2 (14.1.3.768) to enable setting a default value for CMS and Authentication is mentioned, but we are already using this version and I can confirm it doesn't work 
Maybe someone will consider the option to hide to fields and implement at the same time. It is a very useful feature.
Thanks,
Mugur