I must have been lucky, but my experience with BAEC has always been good.
The address can be changed online and I fully understand the reason for not being able to change the address during a six-month window. Actually other airlines have a similar rule.
I have always found my local European call center trying hard to help me and calling me back when they said they would.
A couple of times, I needed to change an award flight when I was abroad and could not do it online and at a time when the European call center was closed. The local center (in those cases Hong Kong) understood the situation and did the change for me.