It is possible for an external app to trigger a refresh of a specific Plex library section rather than the full media server library (ie scan the TV Shows section but not the Movies, Home Movies, Kids TV etc). However the only way to refresh / rescan an individual TV show is through Plex Web and clicking the Refresh button inside a show. This will rescan files on disk and also download new metadata. I don’t think this function is exposed via the API though.
More detail here: