Not much to say here:

Under a post row, a new Reactions hyperlink can be clicked on.
For users with JS enabled, this will open up a modal containing every reaction in the forum. Clicking it adds that reaction to posts.
For users with JS disabled, this, similarly to editing, reporting, and deleting posts, will simply refresh the page with the modal visible on the page there, or something. Or alternatively, more like reporting, will just bring you to a dedicated page containing the same information as the modal.

Reactions would show at the very bottom of the posts, and their number. Clicking on a visible reaction will simply count to that reaction so you don't have to add it through the modal.

My justification:

Some people may agree or like something but shouldn't probably need to make a post saying "this ^^^^" or "I agree with you" <- (without anything else after that. WHY do you agree?), or anything in which we could call "bloat", for true lack of a better word.

Potential problems:

Mainstream websites have devolved into a game of trying to maximize views, and likes. 4chan currently suffers from a problem like this which boils down to a concept called (You) farming, which is the closest to 'views', 'likes' or, in our case, "reactions" that they can get to.

We would need to specifically direct moderation efforts towards stamping out half-assed or 'quirky'/'funny guy'/'class clown' attempts at posting solely for the sake of trying to get large amounts of reactions. Reactions should only be used if you don't have anything substantial to provide to the topic but you want to illustrate your overall emotions towards that specific post without derailing the thread.
^ Maybe users could be asked to type out a reason for reacting, to also prevent threads from being derailed with "hey @fucker829, why did you react to my post with the fucking sad face "?

Could this be a good idea, or a bad idea? Is there anything that could be changed or completely altered about it?

It's not a bad idea per say, but I feel like it may take essence away from the site. Olden forums simply had no case where assigning reactions to posts was needed. This is rather more of a modern feature seen in Xenforo, and I'd even go out of the way to say that those kinds of 'bloat' responses maaaay sort of be beneficial to the forum's current aim and goal right now.

We haven't experienced it here yet, so I truly cannot decide. It's not a problem yet, so we don't need to really try and go solve something that probably won't even hurt us to begin with.

The Cyberix Administrator