Originally Posted by Cargo Cult

I've seen this several times - that and the 'upgrade my class of travel' link. I think that once you go within the T-24 limit for the first sector, BA take ownership of the booking to some extent and you can sometimes make these changes online. Still a bit hit or miss, and even if the link is available in MMB sometimes it will not actually let you complete the change.

The ability to consistently change/upgrade TA-made bookings via MMB before the T-24 slot would be my joint favourite enhancement along with ability to see fare class...