public function filter_rewrite_rules( $rules )
    {

        foreach ( $rules as $rule ) {

            if ( $rule->name == 'display_entries_by_tag' ) {
                $rule->parse_regex = '#^blah/(?P<tag>[^/]*)(?:/page/(?P<page>\d+))?/?$#i';
                $rule->build_str = 'blah/{$tag}(/page/{$page})';
                $rule->update();
            }
        }

        return $rules;
    }