Many of my movie files are in my root Movies folder
…/Movies/MovieName1 (YYYY).mkv
I would like to move those movies in the root to their own subfolders:
…/Movies/MovieName (YYYY)/MovieName (YYYY).mkv
When I have done this and re-scanned the Library Plex was able to locate the file in its new subfolder home and carry on as usual but I wanted to know if this is truly OK to do.
Perfectly ok. You’re basically doing a light version of the procedure described to move media (folders) to a new location. When you do that, take care to disable automatically emptying the trash to avoid Plex recognizing the moves content as new items (e.g. losing edited metadata, ratings, playlist assignments or watch history)