You can see my response in this thread about this change: PMS revert back to old rating from stars
Basically it doesn’t make sense to alter ratings from an external site like IMDB because then it would no longer reflect reality when that rating changes over time as you’ve now made it static.
To update external ratings you should just refresh the metadata for the item. If you want to give it a personal rating then that’s what the star rating system is for.
If you really still need to alter that field for some reason then you can do it via the api, example:
http://localhost:32400/library/sections/:sectionId/all?type=1&id=:itemId&rating.value=7.2&rating.locked=1&X-Plex-Token=:yourtoken
Replace :sectionId, :itemId and :yourToken with appropriate values. Passing rating.locked=1 will lock it so that subsequent refreshes won’t change it.
