node_overview_types no hook? how to customize
Since there's no specific theme function used the easiest way I can think of is to implement hook_page_alter() and alter the table directly. The following code works for me:

function MYMODULE_page_alter(&amp;$page) {
  if (request_path() == 'admin/structure/types') {
    // Get the types, they will automatically be in the same order as the rows
    // in the existing table
    $types = array_keys(node_type_get_types());
    $limit = count($types);

    for ($i = 0; $i &lt; $limit; $i++) {
      // Get the existing row
      $row = $page['content']['system_main']['node_table']['#rows'][$i];

      // Get the type related to this row
      $type = $types[$i];

      // Make a link to add to the table
      $link = l('Link Text', 'my/path/to/' . $type);

      // Make up the new cell. I know there's an easier way to do this but
      // I can't for the life of me remember it right now
      $new_row = array($row[0], $row[1], $row[2], $link, $row[3], $row[4]);

      // Overwrite the existing row with the new one
      $page['content']['system_main']['node_table']['#rows'][$i] = $new_row;
    }

    // Increase the colspan of the header to take into account the new column
    $page['content']['system_main']['node_table']['#header'][1]['colspan'] = 5;
  }
}