It disappoints me when I see suggestions like those in https://communities.bentley.com/products/plant/w/plant_design_and_engineering__wiki/28289/how-to-configure-openplant-modeler-to-use-workspace-from-shared-location when options exist to avoid editing local cfg files.
I was lucky enough to come across this one from one of the Bentley Developers. You CAN use a custom cfg file in the appl directory.
The key here is to use _USTN_WORKSPACEROOT rather than _USTN_INSTALLED_WORKSPACEROOT.
The beauty here is that I now have a much easier way of setting up s file(s) to enable network builds for OPM\OPIM. It also means I now have a basis to have a single file based on variables for OPM\OPIM builds.
Hope that helps in some way.