Change select options within a nodereference

First you’ll have to make use of hook_form_alter() function.

function example_form_alter(&$form, $form_state, $form_id) {
  $form['field_example_reference']['#pre_render'] = array('example_change_node_reference');

Now the node reference will look for a example_change_node_reference() function which will return an array of options.

function example_change_node_reference($element) {
      $element['nid']['nid']['#options'] = array($node->;nid => $node->title);
  return $element;

Make sure you pass the $element variable into the function. More info: