Rebuilding a form

I am trying to rebuild a form in Drupal 7. I know its 'form_build_id' (e.g. form-_eNZLqaZWy7-6kYuGma5Cxg1Gru7Tmr9W2tsofSJxSg)

I defined this hook_menu and menu callback function:

/**
 * Implements hook_menu().
 */
function set_menu_menu() {
  $items['admin/structure/set_menu/rebuild/%'] = array(
    'title' => 'Rebuilt',
    'page callback' => 'set_menu_ajax_rebuild',
    'page arguments' => array(4),
    'access callback' => TRUE,
  );
  return $items;
}

function set_menu_ajax_rebuild($form_build_id) {
  $form_state = form_state_defaults();
  $form = form_get_cache($form_build_id, $form_state);

  $form_state['no_redirect'] = TRUE;

  // @see drupal_rebuild_form()
 
  // I would like to increase number of elements in my form
  $form_state['set_menu']['count']++;
  $form_state['rebuild'] = TRUE;

  drupal_process_form($form['#form_id'], $form, $form_state);

}

I would like to rebuild a form by hitting url like this http://www.example.com/admin/structure/set_menu/rebuild/form-mQVd8FeimUA... - this url displays no error but it does not rebuild my form.

The code never rebuilds any form. Is it possible to rebuild a form this way?

Thank you, Martin.