With Air New Zealand it's built into the airport kiosk check-in process. We had inflexible flights and when I called two days before to see about a change to an earlier same-day flight the price was going to be extortionate (change fee + fare difference). However, on the day it was possible to change to the earlier flight FOC without speaking to anyone at the ticket counter.

I'm not suggesting BA should do it, just pointing out a different approach by the airline of 'Middle Earth'.