/**
 * Implements hook_xmlrpc_alter().
 */
function {{ machine_name }}_xmlrpc_alter(&$methods) {
  // Directly change a simple method.
  $methods['drupal.login'] = 'mymodule_login';

  // Alter complex definitions.
  foreach ($methods as $key => &$method) {
    // Skip simple method definitions.
    if (!is_int($key)) {
      continue;
    }
    // Perform the wanted manipulation.
    if ($method[0] == 'drupal.site.ping') {
      $method[1] = 'mymodule_directory_ping';
    }
  }
}