Regcode support

Showing the field is rather easy; put this code in the complete_profile.pages.inc

  // Support the regcode module
  if (module_exists('regcode')) {
    $code_optional = variable_get('regcode_optional', FALSE);

    $form['regcode']['regcode_code'] = array(
      '#type' => 'textfield',
      '#title' => variable_get('regcode_field_title', t('Registration Code')),
      '#description' => variable_get('regcode_field_description', t('Please enter your registration code.')),
      '#required' => !($code_optional || user_access('administer users')),
      '#element_validate' => array('regcode_code_element_validate'),
    );
  }

Currently trying to set the field when editing information.

Actually validating the code is a bit harder. We overwrite the form submit function to trigger a custom function, where we check if the regcode module exists, and hack us a way to be able to use the defined helper function:

1. Change
$form['#submit'][] = 'user_profile_form_submit';
to
$form['#submit'][] = 'complete_profile_form_submit';

2. Add below

function complete_profile_form_submit($form, &$form_state) {
  // Regcode support
  if(module_exists('regcode')) {
    // Set regcode to used

    // Little hack to be able to use the regcode_use_helper here
    $regcode_array = array('regcode_code' => $form['regcode']['regcode_code']['#value']);
    regcode_use_helper($regcode_array, $form['#entity']);
  }

  // Submit the profile form
  return user_profile_form_submit($form, $form_state);
}

Added patch