While not a direct answer to your question, see
http://www.flyertalk.com/forum/showp...&postcount=169.
In my case the delay was not due to BA / ComAir and they did nothing at all to help. I dont know what they would have done / not done had the delay been theirs.
The only exception that was allowed was changing a connection to a stopover. FWIW, there was no AA involvement in any of these changes. It was all handled by BA / ComAir in JNB.