And it sounds like it's a BAH trip, so one would not want to unravel that trip anyway. But if MAN-LHR is in CE or Plus, then the obvious way to book this is to go for the latest service that's vaguely acceptable and then use FCOD on the day to bring it forward when it is clear how the day will turn out. Changes have to be done more than 1 hour from the new flight (and 1 hour from the old flight) so it could be done by the carousel in Ringway if needed.