How do I remove a validation handler from a form?
Use hook_form_alter() to change the $form['#validate'] to be your custom validate handler.

function custom_module_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  if ($form_id == 'your_form_id') {
   $form['#validate'] = array();
   $form['#validate'][] = 'my_custom_validation'; 
  }
}