D6: How to modify the #theme and #formatter of a field based on build_mode

gistfile1.aw

/**
* Implements hook_nodeapi().
*/
function mymodule_nodeapi(&$node, $op, $a3 = NULL, $a4 = NULL) {
  if ($op == 'view') {
    if ($node->type == 'business' && $node->build_mode == 'mobile') {
      // change the field_photos formatter
      foreach ($node->content['field_photos']['field']['items'] as $key => $item) {
        $node->content['field_photos']['field']['items'][$key]['#formatter'] = 'my_preset_imagelink';
        $node->content['field_photos']['field']['items'][$key]['#theme'] = 'imagecache_formatter_my_preset_imagelink';
      }
    }
  }
}