[Koha] Adding a coded field to the default Unimarc framework

Dear all, I'm trying to add Unimarc field 009 to the default Unimarc framework. I have bulkmarcimported a few records for which this field is defined, and now I'd like this field to be displayed in the OPAC MARC view and in the staff client MARC view. The marc_tag_structure table contains meaningful values. More over, I have tried different values for the tab and hidden colmn in the marc_subfield_structure. However I could never see the 009 field, neither in the staff client's MARC view, nor in OPAC's marc view. Any hint would be very appreciated. Thanks much in advance, Sébastien.