Haven't had to do it for a very long time but iirc:
Open C:\Program Files (x86)\PlayOnline\SquareEnix\FINAL FANTASY XI\USER\ and find the character folder relevant to the macros you want to transfer. I did this by checking the mcr.ttl file in each folder in notepad. This will display the macro book names for that character (ie: when i see 'brd', 'thf', 'nin' in a mcr.ttl i know that folder is relevant to my alt character). Then you need to find out which folder is the desired destination and copy/paste the contents over.
Never been able to make sense of the hex folder names directly ;\