I've been experiencing the opposite lately with the DM line. Agents have been really cool with me snagging an earlier flight (confirmed) when connecting in DTW and ATL. I've been buying only F tix as of late so if there's room up front and I can make the second earlier flight they allow me to swap.
I just did it this weekend TPA-ATL-BHM. Originally had a later flight and landed earlier than expected and snagged 1B on the second leg. Last seat up there.