To clarify this point. Yes, you could update the portal-ext.properties file to bypass the value in the database, but it is stored in the database.
USS stores the EEM host name information in the "PortalPreferences", most of the settings are stored in a single long string. In my system the information is stored in the "preferences" column for portalPreferencesID 10160. Make certain you make a backup prior to editing the database.