I would not hold my breath about the bag making the "new" flight. Bring it to the attention of the gate agents for the new flight and they'll do their best to get your bag on the earlier flight. Given how many people are likely changing flights at DFW right now I would think baggage is a total CF.

I'm surprised the app even let you make a change given that you checked a bag. That will disable SDC for sure but I guess IROPS changes are allowed.

-RM