OpenPLANT PID has options for storage of assemblies in Assembly Manager. These options are to store the assemblies in a System, User or Project location. It is possible to disable these options so the users will only have the Project location available or just the System folder location available. Depending on preference.
To remove these folder options simply remark their storage pathing in the following files:
OPPID DGN Assembly Paths and their locations
For example if the requirement was to hide
Open the Pid.cfg file and remark the following line out.
This will turn off the System option in OpenPLANT PID so the drafters will not even have the option to store assemblies in this location.