I'm sure this is probably a dumb question, but is there ever flexibility on allowing a same day change to the previous or next day?

I need to fly out either last flight of the night or first flight the following morning. My schedule is unclear right now. I would have been happy to rely on the SDC policy, but know it says the new flight must be on the same calendar day. So, instead, I booked reservations for both flights but they were flagged as duplicate reservations.

Now I am forced to cancel one or the other, and possibly be forced to rebook last minute and eat the maximal fare difference on the day of travel. SDC seems intended to add flexibility in moments like this. I can appreciate the program needs to have some boundaries, but I am unsure what to do in this case.

Any advice on the best way to manage flexibility in a situation like this?