Hello,
So my suggestion is: when you rename a title in Plex, it should override the metadata name for the file.
I have ran into a behavior where I rename a movie in Plex and a day later it’s back to its original name even if it was never matched through an agent. I went through the files one by one on the actual hardware device (nas server) and renamed the files. Then told Plex to refresh the meta data and this did nothing in terms of title. And it still kept overriding what I write as a title after a few minutes to a few days. I really enjoy Plex, it has made life really easy and if this feature were to fix my issue. I would love Plex even more!
I have tried that as well and it has still reverted back to the original title name. So most the movie I have I copied from my disks. So the program I used puts _title_23 or something along those lines. I have erased that part many times in plex and the outcome remains the same. It reverts back to the original title. Even though the actual file name doesn’t have that part in it anymore. Only the metadata of the file shows the extra title part.