Originally Posted by
ifu05596
do these flights need to be booked with BA directly or it work if booked via Amex Travel, Expedia etc?
Corporate travel, including Amex and Expedia Business (Egencia) certainly works, though for complex reasons connected with "know your passenger", you need to make changes via BAEC and BA.com rather than the App, otherwise you'll get stuck on "please confirm the credit card number" question.
On Amex public, I have no direct experience, but I would be fairly confident that also works. Expedia I have my doubts in terms of online management, but if it was correctly sold as a Plus fare (or the limited number of CE tickets with this option) then at worst it could be changed at the airport. If pushing out to a later service than booked then you best telephone a BA contact centre at least an hour before the original departure.