Thanks for the replies. Should I phone the BAEC line to confirm do you think or just wait and see if check in goes without a hitch.

Apologies for the unclear first paragraph. Basically I was initially booked to fly EDI-LHR-MIA-CHS in one journey on Saturday. I am now flying EDI-LHR on Friday and LHR-MIA-CHS on Saturday. And yes I'm on BA209!

I'll check with agents at EDI to make sure there are said "no show protect" notes on the booking and constantly refresh the app on Saturday morning to make sure nothing is cancelled!