Giuliano,
if you try to open the .ncd file with Notepad it states it is an XML 1.0 file. Actually, if you open it up with MS Internet Explorer you should be able to see exactly the same structure you see in MAX.
So, if you want to modify and/or create the .ncd file externally you can use a text editor or an XML parser to write your .ncd files and then load the messages from MAX.
Greetings
AlessioD
National Instruments