Thanks for the variety of comments.
We will accept flying the day before. Other options will all end up as a much more complicated journey.
I did tweet CX but they referred me to BA.
Today I will phone BA Silver line to ask for the HKG-TPE flight to also be moved back a day. The are plenty so hopefully be no difficulty for a redemption booking.
I would prefer this to be a UK call centre so best time to call?

I love they way airlines can do what they want more than 14 days out, at my extra cost, but it doesn't work the other way.