I think for sure IF I were to call BA again for other changes I would state at the outset that from my previous experiences I need to speak to agents in Manchester ...
But hopefully somebody with more knowledge and experience of BA RTW tickeing might be able to advise us ....

I have not yet posted my report of arriving and departing Cairo but will try to get i done asap
but in short I arrived Qatar from Doha to Terminal 1 and had someone Meet and Assist for 20USD and I was through in minutes ... the guy took me to the shuttle bus to Le Meridien and I was in the hotel for my overnight stay within 20 mins of landing
The next day the shuttle took my to Terminal 2 which is v close by and you could probably walk there via Terminal 3 I think
Terminal 2 is very swanky and new and quite and empty right now - endless checking of documents and bags but all fine - and although they are still working on the Terminal the Lounge area was more than adequate for a brief visit
Food offerings not great but very attentive and helpful staff
Super fast wifi and v nice toilets
So all in all a very pleasant and stress-free experience - I wasn't hassled at any point
Whether things will change as more airlines move to Terminal 2 .....

Cheers