I'm new here and recently starting using Plex Media Server so my apologies to the mods / devs in advance if this type of thing is not allowed, but I've seen a lot of people complaining about the cast not being editable.
Note - unless you've edited code before I wouldn't recommend you do this, although it's very simple and basically find and replace. Of course make sure to make a backup copy of the original file but as long as you only change the 2 numbers I reference below, you should be fine. Also, I DID NOT have to re-start Plex Media Server for this to take effect, just had to refresh the page.
This was really bugging me as I use Plex/Web a lot and it would only show 2 genre tags and 3 cast member tags. Well it turns out there's a simple change in a JavaScript file to edit the # of "maxTags" for those 2. What happens is when it pulls the MetaData from TheMovieDB it pulls the actors in the order in which they're added to the website, but sometimes you miss some of the bigger actors in the movie because they're listed outside of that top 3. Luckily all of the actors and genre tags are scraped and added to the database, so it's simply a matter of displaying them in Plex/Web.
model:this.model,key:"actor",tags:n,maxLen:50,maxTags:3
model:this.model,key:"genre",tags:i,maxLen:50,maxTags:2