Your asking a mod question though and as I have responded this is not a support question. We have functional checkboxes dropdowns radio box addtional fields for categories in Admin => Edit Categories which you can use. They are not searchable though on the search page not how they are designed.
If you continue to want to modify the existing 6 extra fields per category which are searchable on the search page you would need to properly modify the templates to make those input boxes what you want. This would be something you post outside support in THE MOD CORNER. Depending on what your trying to do you might have modifications to make to PHP files etc
This provided you links on how to properly code an input or select box
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This should explain our company policy on code hacks http://www.photopost.com/forum/showthread.php?t=121154