Related guide: source-modeler-overview.
Edit model sets defaults for the whole .hsm file: catalog connection, namespace, optional default database, and notes used when publishing tables, queries, JSON, and pipeline sources.
Catalog connection is a dropdown of project data catalog connections. Default data type mappings is a comma-separated list of profile names. Select fills it from existing profiles. Edit opens the one named in the field, asks when several names are listed, and creates a profile when the field is empty. A named Configuration hides these fields; edit them on that metadata object instead. The metadata editor has the same catalog dropdown and the same Select and Edit buttons.
Individual cards still override catalog source names. Use Push to catalog on the toolbar after the model checks clean. Check model reports when a published catalog feed is stale vs the card you just edited. Saving the file also offers to publish those stale feeds unless you turn the reminder off (Don’t remind me after save, or Configuration → Hopper EDW).