Aside from the magic trick of applying non-refundable funds to a refundable fare turning the refundable into a non-refundable being a problem... (BTW, it's buried in the rules for the original non-refundable tix.)

Good luck trying to find a refundable ticket cheap enough to try it with after you hand over the $100 change fee. (Yeah, they might be out there somewhere but they sure aren't making them easy to find. You'd think if they wanted to sell them that they'd be just a little more accessible!)