Problem with rewrite_rules_array

Hi Guys,
I want to use add_filter function as rewrite rule (.htaccess). So, I have the following Code:

add_filter(‘rewrite_rules_array’,’addCustomPage’);

function addBuscador($rules){
$newrules = array();

$newrules[“mynewpage/([^/]+)?$”] = ‘index.php?p=13 keyword=$matches[1]’;
$rules = $newrules + $rules;
return $rules;
}

But when I go to my url http://MySite.com/mynewpage/somthing WordPress is redirecting to index.php?p=13 (Appears the address http://MySite.com/index.php?p=13 in my browser) and is not working as htaccess rewrite rule.

Could you help me? is possible that the function add_filter works as .htacess rewrite rule?

Thanks,