No way to correct booking mistakes

I made a mistake yesterday, booking a codeshare flight operated by Iberia, rather than a British Airways-operated sector. With all the fluff about travel insurance upsells and carbon offsetting it was a fairly easy mistake to make, but it was my mistake.

I called BA back less than 24 hours later, hoping to change to an earlier or later BA-operated flight, but was told this would cost £40 per passenger - no exceptions. Apparently the carrier operating the flight is immaterial. This seems a bit hypocritical when they spend money on stuff like this.

I'm a loyal BA customer. I choose them over budget carriers despite a considerable price difference because I value the in-flight service. I don't take that view about many full-fat carriers, and certainly not Iberia.