I got one idea how to make the "HIS Central" / "Local Metadata cache" option more intuitive to use:
The locally registered web service is really an extra "Data Source". Following Tim's suggestion in today's phone call:
1) Rename the "Web Services" search criteria to "Data Sources"
2 On the bottom of the panel add an option "Add Data Source.." or "New Data Source.."
3. This will launch the existing "Service Management" dialog for adding an unpublished WaterOneFlow service URL
4. after downloading metadata from the service, the "Keyword" list and keyword tree is updated by adding an extra node to the tree view
(Note: if the variable names in the registered service follow the ODM controlled vocabulary convention, then no extra keywords need to be added to the tree view)
Please comment if this is a good suggestion