called again, and had a very knowledgable agent. Apparently, the fare rule is jdn0yn0, but he still said that if the return leg is changed after the first leg, the new fare should apply even using the historical fare because the historical fare applies to the first leg and the return leg must be repriced. He did find the fare rules and the actual fare, he was quite shocked about the amount I paid. I have no idea how these things work, but I am just too tired dealing with them as I don't know how to explain it. I certainly cannot say someone on a forum said I shouldn't paying extra for changing lol