It is the UK office for Ireland, so you can just ring the UK number. If it's quiet and you know exactly what the change needs to be, then just drop an email with a short version and they can do it that way.
[email protected]

That's supposed to be used for things say 1 or 2 days away but I'm sure they are OK to do something simple and quickly.

For simple flight switches, I think many BA agents can handle that, it doesn't need to be BAH - that includes the GGL helpline and email.