One piece of advice: Do not select the same seat for both flights. There was a time in the past where, on a through flight, you could deplane at the intermediate stop and ask the GA working that flight for a seat change. Assuming the GA could do that, it would force the DL's computer to treat that as two separate segments.

Not sure if that works since the merger, but selecting a different seat for the return flight is a precaution I would take.