Yes, but that only addresses the second point. Also thetvdb.com often locks data for television shows, preventing users from editing the content.
Yes, thetvdb will do that and I too find that very frustrating. The suggested action then is to message an admin and plead your case. 
As for the first part, you may have to be the one to gather and create the new information and add it to either web-site.
My use case is for home/family movies. You can use the cast field to essentially tag those who are in the videos (nieces, nephews, parents, siblings, etc.) You can then easily click the cast member names to see all other videos containing said person. Obviously this is stuff I can’t upload to any third party site.
Interesting use case and definitely one where access to the cast listing would be great.
I wish this was implemented, i’m already looking how to edit the .db file just to get this done. Please add this feature.
+1 Very good suggestion! I agree for this request.
I see others have thought the same. We need to be able to add and remove people from movies, shows, and episodes. That way I can just search say Riann Steele and it lists everything she’s in that’s in my collection.
A while back I wrote my own custom Agent that populated cast metadata for my movies. It won’t satisfy everyone’s use case. My specific use case was having a collection of home movies (which you’d never find or add to sites like The Movie Database, or IMDb) that you would add family members to as cast members.
Also since my target audience was myself, I didn’t do extensive testing. Once it got to a point where it worked, I stopped messing around with it. Saying that, if you decide to try it out, let me know if there’s any issues, and I’ll try to fix it when I get around to it.
Second, this is the first thing I ever wrote for Plex, and largely worked off of other examples I found on GitHub. If you ask me why I’m doing things a certain way, there’s a good chance I can’t give you a good answer.
Here’s the project: https://github.com/mistercam/TextFileMetadataAgent.bundle
Take a look through init.py to see what I’m doing. I think it’s fairly straight forward. Download it, unzip it, and drop TextFileMetadataAgent.bundle into the Plex plugins directory. Restart Plex.
You then have to activate it through the Agents screen in the server settings.
If you want to set cast data for your ChristmasRecital.mp4 video file, in the same directory, create a file named ChristmasRecital.mp4.txt
Inside that text file you can specify a line like:
CAST=Sally,Doug,James,Lizzie
When you create a new “Personal Media” movie library in Plex and add the source directory, the cast should be populated.
Also, thanks to @ZeroQI and @agentplex007 . ZeroQI pointed me to some starter files for the plugin, which helped a lot. I also borrowed some code posted by agentplex007 a while back in reply to someone else.
Again!!!
Here is another 3 year old request that makes too much sense for a media server/player.
WHY will Plex not add meaningful features that relate to the CORE FUNCTION of their flagship product???
I have many movies where the media match gets NO cast members added.
So not being able to edit that makes searching or filtering by actor useless.
I have a couple of examples.
Like the Segal movie “Under Siege”
No matter how many times I match, fix incorrect match, etc. The cast is never added.
So if I search or filter on Segal or Busey this movie never appears.
Hence Search and Filters do not work properly either.
Search and filter functions are BASIC to a media server/player system and Plex fails horribly at this.
Come on guys.
Get with the program and get down to biz!!!
Who the hell is running this show anyway. The guy who decides release contents needs to start looking for another job IMHO!!!
I the old days I would have been fired for this kind of release management…
I would bet it I requested that Plex would add the feature to bounce my media off TelStar… It would be in development already!! LOL (And of course. It would stay in Beta for years, be full of bugs when released, and never fixed!!!)
Definitely should be able to edit actors
I agree! Can’t believe this isn’t already in there to be honest
Fun Fact. Did you know that Colin Farrell, born in 1976, was very mature at a young age! In 1977 he played Cpl. Hancock in A Bridge Too Far. I did not know that until today. Thank you, Plex!
Oh, wait. It fixed the picture after I refreshed the data, but when I click on the picture of British Colin Farrell in the cast it still takes me to all of the movies that Irish Colin Farrell is in. Maybe this is beyond the scope of this request, but being able to edit the actor ID is probably a legitimate addition, as well. Regardless of which of the Colin’s i click it sends me to:
filters=actor%3D17315&filterLabel=Colin%20Farrell
and now that the data refreshed in A Bridge Too Far this is what the cast looks like in Crazy Heart:

Haha, I want the old (young) Colin back!
I would like to upvote this request as well. I added Dr. Horrible’s Sing-Along blog to my collection, as a movie, but the Movie Database only has it listed as a TV show. When I tried to scrape it with Plex, it pulled the Making of instead of the actual title. I had to manually add the metadata to keep it in my movie collection, which means there is no cast listing. Would love to be able to add/edit cast listings manually.
This has recently become even more important as a lot of Stephen King movies I have - which were originally broadcast as 2 or 3 part miniseries on TV, are no longer listed as films on The Movie Database. Which means that all the metadata now needs to be manually added in order to keep these films in my movies collection. Obviously this means there is only so much I can do, and the cast list will always be empty. I’m also interested as others are - in adding a “cast” to my home movies.
I agree.
We have been able to edit the Writers/Directors fields for a long time, but not the Actors field.
I hope that will be possible soon.
Yep. Would like this feature.
I’d like this feature as well
Just adding my 2c that I’d like to see this feature. I guess most of us carefully curate and maintain their media library so being able to edit this would be brilliant (and kinda surprising it’s already not become a feature; how hard is it?).
Plex has provided incorrect Cast and Gene as GlowGaze.com for these below movies, please Plex Admin to update them with correct information asap.
The Amazing Spiderman
Compulsion
Disconnect
Empire State
Erased
The Great Gatsby
Man of Steel
Now You See Me
Oz The Great and Powerful
Parker
World War Z