Bulk registration or disallow registering of certain usernames
You can do this by code, alter the registration form (hook_form_user_register_form_alter), in a custom module like:

function MY_MODULE_form_user_register_form_alter(&amp;$form, &amp;$form_state, $form_id) {
    $form['validate'][] = 'reserved_usernames';
}


And then implement the validation (in the same MY_MODULE.module file) method like:

function reserved_usernames ($form, &amp;$form_state) {
  $reserved = array();
  $reserved[] = 'reserved_name';
  $reserved[] = 'reserved_name_1';
  $reserved[] = 'reserved_name_2';
  $reserved[] = 'reserved_name_3';
  $reserved[] = 'reserved_name_4';
  $reserved[] = 'reserved_name_5';

  if (in_array($form_state['values']['name'], $reserved)) {
    form_set_error('name', t('The name %name cannot be taken.', array('%name' =&gt; $form_state['values']['name'])));
  }
}