You can add new fields in the category.def. When you do this, I would highly recommending saving a back-up of your categories.db file.
There is an upgrade file that you can use that will automatically create the new filed in your categories.db file.
Search this forum for "upgrade" and there should be other threads that will help you.
Regards,
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Eliot Lee
Founder and Editor
Anthro TECH, L.L.C
http://www.anthrotech.com/
info@anthrotech.com
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Coconino Community College
http://www.coco.cc.az.us/
Web Technology
Coordinator
elee@coco.cc.az.us