Originally Posted by
3Cforme
1. One can not combine classes of srvice between origin and destination. Any premium class segment makes the one-way journey premium; any medium or high award level segment makes the entire one-way journey medium or high.
One could, however, choose to sit in the Y cabin on one segment if the there is space available. The mileage deducted will be the premium cabin mileage.
3. Same Day Change is permitted for $50 on award tickets. DL offers no free standby for non-elite/Silver.
SDC is officially not allowed on international itineraries so I wouldn't count on it. You may be able to make the case at the airport upon arrival in DTW. No guarantees though (and your best bet is to request the SDC in the SkyClub - or you can try before re-checking your bags after clearing customs).