With so many same-named actors, tagging them by merely a string won’t be of much help — especially with the default agents doing a good job to pull cast & crew information from their metadata backend.
That being said… Plex will recognize embedded metadata tags listing actors. This can be helpful to tag family members in home videos. It won’t help much with regular movies / shows as such manually tagged items won’t merge with actors pulled from online metadata sources.
If you’re super desperate about manually tagging these things, you might want to check out the NFO agent preview.
