Note: After saving, you have to bypass your browser's cache to see the changes. Google Chrome, Firefox, Microsoft Edge and Safari: Hold down the ⇧ Shift key and click the Reload toolbar button. For details and instructions about other browsers, see Wikipedia:Bypass your cache.
$('head').one('reftoolbarbase', function() {
CiteTB.UserOptions['date format'] = "<monthname> <date>, <year>";
});