Originally Posted by
Antarius
You can get a refund, but changing to a later flight may cause additional charges
See this
I believe that is part of the T&C for international tickets, not domestic (as discussed in a similar thread). However, I have used it successfully several times when a 77W was swapped for a two class 321 on LAX-MIA. Not sure if my status made a difference.
It's good to have that section available to cite.