[Zope] newbie question CMF/Plone

[Fabien Nkundabagenzi]

Hi,

Can anybody tell me how to edit a portal_type (like File) to be able to add
new properties (metadata) (for example: "geofocus") to the file using
CMF/Plone ?

Simply adding additional metadata doesn't seem to work. I tried modifying
the File.py and the DublinCore.py scripts to include additional entries, and
the file_edit_form as well. But when a try to add a File type, it returns
the message :

Dating not found in 'request/geofocus | here/Geofocus'

What else should I do ?

Thanks,

Fabien.