<?php
   $info_box_contents = array();
   $info_box_contents[] = array('text' => sprintf(TABLE_HEADING_NEW_PRODUCTS, strftime('%B')));

   new contentBoxHeading($info_box_contents);

   if ( (!isset($new_products_category_id)) || ($new_products_category_id == '0') ) {
     $new_products_query = tep_db_query("select p.products_id, p.products_image, p.products_tax_class_id, if(s.status, s.specials_new_products_price, p.products_price) as products_price from " . TABLE_PRODUCTS . " p left join " . TABLE_SPECIALS . " s on p.products_id = s.products_id where products_status = '1' order by p.products_date_added desc limit " . MAX_DISPLAY_NEW_PRODUCTS);
   } else {
     $new_products_query = tep_db_query("select distinct p.products_id, p.products_image, p.products_tax_class_id, if(s.status, s.specials_new_products_price, p.products_price) as products_price from " . TABLE_PRODUCTS . " p left join " . TABLE_SPECIALS . " s on p.products_id = s.products_id, " . TABLE_PRODUCTS_TO_CATEGORIES . " p2c, " . TABLE_CATEGORIES . " c where p.products_id = p2c.products_id and p2c.categories_id = c.categories_id and c.parent_id = '" . (int)$new_products_category_id . "' and p.products_status = '1' order by p.products_date_added desc limit " . MAX_DISPLAY_NEW_PRODUCTS);
   }

   $row = 0;
   $col = 0;
   $info_box_contents = array();
   while ($new_products = tep_db_fetch_array($new_products_query)) {
     $new_products['products_name'] = tep_get_products_name($new_products['products_id']);
     $info_box_contents[$row][$col] = array('align' => 'center',
                                            'params' => 'class="smallText" width="33%" valign="top"',
                                            'text' => '<a href="' . tep_href_link(FILENAME_PRODUCT_INFO, 'products_id=' . $new_products['products_id']) . '">' . tep_image(DIR_WS_IMAGES . $new_products['products_image'], $new_products['products_name'], SMALL_IMAGE_WIDTH, SMALL_IMAGE_HEIGHT) . '</a>
<a href="' . tep_href_link(FILENAME_PRODUCT_INFO, 'products_id=' . $new_products['products_id']) . '">' . $new_products['products_name'] . '</a>
' . $currencies->display_price($new_products['products_price'], tep_get_tax_rate($new_products['products_tax_class_id'])));

     $col ++;
     if ($col > 2) {
       $col = 0;
       $row ++;
     }
   }

   new contentBox($info_box_contents);
?>

  if ( (!isset($new_products_category_id)) || ($new_products_category_id == '0') ) {
    .... // donc le code défaut si pas de catégorie
  } else {
    // c'est cette partie de code que tu dois remplacer par la fonction redondante que tu as créée + créer l'affichage que tu appeles plus bas à la place du fetch_array de la requête, toujours bien entendu en testant si l'id de la catégorie existe (auquel cas on affiche juste l'affichage créé ici) ou pas (auquel cas on fait le fetch_array de la requête).
  }