Hello ​@jayartibee, welcome to the Sonos Community!

If one adds a track to an iTunes (‘Music’) playlist on a device running the Sonos App will it update a Sonos ‘Imported Playlist? 

Any change you do to your Music Library will require you to update the music library index on Sonos before these changes will appear in your Sonos app.

Please have a look at our Support Article Update your Sonos music library which includes information on how to do so.

If you make changes to your music library often, you can schedule automatic index updates. Once setup, Sonos will scan your library for changes once a day at a specified time.

Note that the computer or NAS drive where your library is stored must be powered on and awake at the specified time for the index update to be successful.

I hope this helps.