PROBLEM
When a filter is created to manipulate worksets, it manipulates worksets within linked files, not the workset the link file may be on.
CAUSE
Worksets within a linked Revit file are accessible from the project file.
SOLUTION
This can be done manually via:
Insert > Manage Links > Revit > select the link to modify.
Manage Worksets > Select workset name.
Set Opened to Yes or No through the Open or Close buttons. Click Reload when finished.