It’s very strange how there’s such variation in other people’s experiences in changing their 50% avios booking. I’ve got an involuntary change due to a cancellation on BA27 on the 29th of this month, and yet, when I try to change it online, the outbound says that there is no availability whatever the day I have picked. I seem to tick all the boxes (rebooking within a year, involuntary change) but it doesn’t allow me to rebook at all. Very curious as to what the limitations are to this.