The agent I spoke with about 11 hours ago told me there was no fare difference and no change fee since it was refundable (referring to change fee of course). I'm still on hold with united.com. Let's see what they say.

Update: The agent I spoke with earlier did not properly "exchange" my ticket. The united.com rep took a while, but exchanged the ticket, and I'm now able to check-in online. Just goes to show you that good agents make all the difference. Thanks to the ICC rep I just spoke with ^