Kato's suggestion is a good one. I have never used moneo but it should be able to do what you are looking for.
If you where just looking for the custom .utc files that are in the module. You do not even need a modunpacker program to do that. all you have to do is open the module in the toolset and all the files in the module are unpacked into the temp folder in the modules folder. The resref's for the creatures will be the filenames for the utc files.
If you still want the file formats they are here>>
http://nwvault.ign.c....Detail&id=1501
The GFF format was somehow missed being placed into the original download. I do see that he has added it as a spereat download. It is that format that you will have to understand to script anything for the files. The files themselves are normaly packed together in an ERF format that covers the .mod file and any hak's . If you are going into the bif's you will also need to learn the Key/ bif format.
If you are going to also get a list of creatures that are in haks in the module a list of the haks attached to the game will be in the info(.ifo) file.
There was a not so good explaination on the gff format in >>
I need a clearer GFF/BIC file format explanation It was just the best I could do.
Hope that helps if you still plan on scripting it yourself. moneo would be the best solution if it works for you.