Classifieds main section, edit Default display content

Ont he main classifieds screen, I would like to edit the core plugin files, in order to include a custom field, namely

http://sanaps.org.za/classifieds/

I would like to add the custom field " auction date "

Currently : TITLE , POSTED BY, CATORGARIES

I do understadn that I have to amend the lopp-taxaonomy.php,
And that furtehr plugin updates can disrupt this.

Please do assist in adding the custom field to be displayed.