Using 'request' filter with 'wp_ajax_query_attachments' action

I’m trying to change the query_vars that worh worh ajax request. The action resides in wp-admin/includes/ajax-actions.php at line 1808. The do_action resides in wp-admin/admin-ajax.php

One or the other way, I can’t get the query_vars to change :S While the changing of query_vars does work when it’s non-ajax.

add_action('wp_ajax_query_attachments', 'hook_to_request');

function hook_to_request() {
    add_filter( 'request', 'change_request' );
} 

function change_request($query_vars) {

    // do something with the query vars

    return $query_vars;
}

Is there anyone who can shed a light on this ??