Changed my BA Holiday flight (PRG-LHR, Economy Plus) using FCOD to the (horribly) early one over the phone today. The agent responded 'Why would you do that to yourself?' Took less than a minute.

It looked like there were about 20 seats available for my intended flight on ExpertFlyer, so it got me thinking I could actually phone whilst on the way to the airport to change (assuming I'm >1 hour from departure), instead of ruining my night of sleep further by calling around 1 CET (midnight GMT). Might try if the situation comes up in the future.