The problem with NEBS Form Magic Deluxe is its availability. The Internet doesn't offer anything about it, just some websites that still mention its name which could mean that NEBS Form Magic Deluxe is now a discontinued application without any form of support and development as well as troubleshooting.
Therefore, look in the installation directory for Help files that will provide a better explanation as to why you can't change a customer's address.
Try accessing the built-in Help from the main menu bar as well.