There is no way to change the date of departure without cancelling/rebooking (and paying a change fee). (Occasionally they will be accommodating if you change a redeye, like from an 11PM departure to 12:30AM the "next day.") Can you get internet access on the flight and be "on call" that way? Your other alternative is to do a Same Day Confirmed, but that will probably be a mess because it's not at all clear you could find a later flight DFW-NRT.