Changing widget item

How to change filefield widgets` item type (textfield to textarea) correctly. I mean, without changing filefield_widget.inc

 if (!empty($field['description_field'])) {
    $element['data']['description'] = array(
      '#type' => 'textfield',
      '#title' => t('Description'),
      '#value' => isset($item['data']['description']) ? $item['data']['description'] : '',
      '#type' => variable_get('filefield_description_type', 'textfield'),
      '#maxlength' => variable_get('filefield_description_length', 128),
    );

every time the module updates?