This has likewise happened to me before (the unannounced schedule change). Typically, I have been able to change the flight to whatever other routing is available on the schedule without any change fees whenever the proposed flight is substantially different from my original flight (obviously, you aren't going to get any sympathy when it's only a 15 min. difference!)

Sometimes they put me on hold on the phone to get a supervisor to ok the second change, but never been turned down flat once I explained that *NWA* picked the schedule, not me.