Pls save the gigantic post I'm making make if I accidentally click a link I put in it.

I don't see how Riot could do that on their end, as they don't receive any data from your post until you hit post. There are programs like Lazarus that save text that was typed into forms like what you use for a post.

On the old forums my entry box usually saved itself if i moved back by accident.

I don't know how that actually works, but it did it.