I'm not aware of a way to prevent notifications for a specific forum thread/post.

Example: In a followed game, I want to receive notifications for all forum threads/posts for that game except for a specific troll thread/post.

Is it possible to get a "Unfollow Thread" option to allow this functionality?

No

let me guess, you want to remove the notifications from the super mario 64 forum chain threads? :)

I dont think that notifications for threads are a good idea in games like that. You cant disable notifications from specific threads