Either you or your friend have the details wrong. Anybody can change their ticket on WN for any reason or for no reason at all. They pay the fare difference and that is it. If there is a cheaper fare, they get the fare difference back in cash or as a credit depending on the type of ticket they originally held.

All of this is, of course, dependent on the availability of a seat.

You should check back with your friend and confirm the facts as what you have reported here is simply not accurate.