How to avoid that a module encodes json puts out "\u0026" instead of "&"?
Explanation:

Content as Json module simply returns the content by running it through drupal_json_output(), which in turn call drupal_json_encode().
Inside drupal_json_encode drupal ensures to have unicode conversion to special characters including '&lt;','>','&amp;'.

function drupal_json_encode($var) {
  // The PHP version cannot change within a request.
  static $php530;

  if (!isset($php530)) {
    $php530 = version_compare(PHP_VERSION, '5.3.0', '&gt;=');
  }

  if ($php530) {
    // Encode &lt;, &gt;, ', &amp;, and " using the json_encode() options parameter.
    return json_encode($var, JSON_HEX_TAG | JSON_HEX_APOS | JSON_HEX_AMP | JSON_HEX_QUOT);
  }

  // json_encode() escapes &lt;, &gt;, ', &amp;, and " using its options parameter, but
  // does not support this parameter prior to PHP 5.3.0.  Use a helper instead.
  include_once DRUPAL_ROOT . '/includes/json-encode.inc';
  return drupal_json_encode_helper($var);
}


If you see if your php version is greater than 5.3 than json_encode() it self takes the argument to make sure all are unicode converted, it php is less than or euqall to 5.3, than drupal imcludes a helper json-encode.inc file which do the same.

Solution:

Way 1: The best would be to handle it on the client consuming the json data, have quivalent parser on the consumer side as well.

Way 2: Hook into contentasjson module to return json the way you want.Alter menu callback to register your own page callback

function mymodule_menu_alter(&amp;$itmes) {
  $item['contentasjson/%/%']['page callback'] = '_my_custom_json_as_content';
}

//Copy the code as it from contentasjson module `contentasjson_get_data()` callback with a small change the json_encode function.
function _my_custom_json_as_content($type, $id) {
  switch ($type) {
    case "node" :
      $data = _contentasjson_get_node( $id );
      break;

    case "comment" :
      $data = _contentasjson_get_comment( $id );
      break;

    case "menu" :
      $data = _contentasjson_get_menu( $id );
      break;

    case "taxonomy_term" :
      $data = _contentasjson_get_taxonomy_term( $id );
      break;

    case "taxonomy_vocabulary" :
      $data = _contentasjson_get_taxonomy_vocabulary( $id );
      break;

    case "custom_data" :
      $data = _contentasjson_get_custom_data();
      break;

    default :
      $data = _contentasjson_get_error_message_type( $type );
      break;
  }

  // If false (no data object returned), generate return message
  $data = ($data == FALSE ? _contentasjson_get_error_message_id( $id ) : $data);
  // Here is the small change we are doing.
  json_encode( $data );
}