I can do it by hard coding the file qa-app-format.php in Core, line 1098
Orginal Code
[php]
$navigation[($page['flags'] & QA_PAGE_FLAGS_EXTERNAL) ? ('custom-'.$page['pageid']) : $page['tags']]=array(
'url' => qa_html($url),
[/php]
and my code here
[php]
$navigation[($page['flags'] & QA_PAGE_FLAGS_EXTERNAL) ? ('custom-'.$page['pageid']) : $page['tags']]=array(
'url' => '?qa='.$page['tags'], // changed here
[/php]
Problem solved but I prefer to do it via plugin (if I can overide the qa_navigation_add_page function) rather than hard-coding it.