If it's any consolation I had a flight change on a BA/AA itinerary (also via DFW) which was booked with BA direct, the change extended my layover at DFW from 4 hours to 5:30 hours which wasn't ideal as I'll be staying at the airport. There was a flight which departed 30 minutes after my original scheduled flight but BA would not rebook me as the original flight wasn't cancelled just retimed so BA wouldn't budge. You haven't lost anything by going via Expedia, BA would have treated just as bad!