Answer
For the database side specifically, updating the DB connection string through the Admin Console is really the only step needed — if the Admin Console itself isn't reachable at the usual application URL after the IP change, that access path needs to be restored first (rather than trying to bypass it) before making that connection-string change. For the Middleware Server side more broadly, rather than manually hunting down and editing every .xml/.properties file that might still reference the old IP (which isn't reliable and isn't a supported approach for a customer installation), the cleaner path is recreating the IFS Home instance based on that environment's own XXXX_configuration.xml file, which regenerates the instance's configuration consistently from a single source of truth instead of patching scattered files individually.