Alter message status per content type
I suppose you want to show a message after submitting the form. (But as Pierre commented, please be clear in what you want and do not make us assume things.) hook_form_alter() works during the building of the form. Your code probably works, but there is no message generated yet. 

Instead, use hook_form_alter to add a new submit callback and place your code in there. Somewhat like this:

function alter_appointment_message_form_node_form_alter(&amp;$form,&amp;$form_state,$form_id)
{
  $form['#submit'][] = 'alter_appointment_message_post_submit';
}

/**
 * Custom submit callback.
 */
function alter_appointment_message_post_submit($form, &amp;$form_state) {
 if($form['#node']-&gt;type == "appointment_request") {
   drupal_get_messages('status'); // Flush default simplenews status message
   drupal_set_message(t('An appointment has been requested'), 'status');
 }
}