This is an extension of this question:

Need help with AJAX callback function for text field validation in form_alter

I have a form with a Username autocomplete field (txn_user). The editors want to be able to enter a UID (txn_userid) as an alternative way of specifying the User for the form. They want to be able to enter the UID and skip the Username field altogether.

So in my form validation function, I want to be able to disable the required property (and all other validation) of the Username field during a Submit IF the editor typed in a UID field. In other words: the UID field should ‘short-circuit’ the Username field.

This is what I have so far (which doesn’t work, obviously). Or do I need to do this via AJAX or straight JS?

function _validate_add_userpoints_userid(&$form, &$form_state) {     $values = $form_state['values'];     if( $values['txn_userid'] ) {         $newuser = user_load($values['txn_userid']);         if( ! $newuser) {           form_set_error('txn_userid', 'You have entered an invalid UID. Either leave this blank and select a Username or enter a valid UID');               }     else {           // this part works... the User Name is properly assigned.         $form['txn_user']['#value'] = $newuser->name;                $form_state['values']['txn_user'] = $newuser;          $form_state['input']['txn_user'] = $newuser->name;                    // this part doesn't work... the User Name field is still required on submit.         $form['txn_user']['#disabled'] = TRUE;         $form['txn_user']['#ajax_processed'] = TRUE;         $form['txn_user']['#required'] = FALSE;         $form['txn_user']['#needs_validation'] = FALSE;                  unset($form['txn_user']['#process']);     } } 

}