Firstly, thank you for taking the trouble to read this.

Would anyone know if it is possible to change the frequent flyer number on a JAL domestic flight?

I have booked a return, domestic award flight via the JAL website (HND-CTS-HND) and the JAL website is so clunky for its domestic award flights that I can see no obvious way of changing my current JAL FF# (I had wanted to add my BAEC Gold number to my booking instead). I have tried Finnair and RJ.com sites in order to try to make this change, but to no avail, perhaps because they don't recognise JAL domestic flights?

Would anyone know if changing FF#s on a JAL domestic flight is even possible online?

Many thanks in advance!