Swap theme according to page

<?php
/*
    Plugin Name: Trocar Tema
    Version: 1.0
    Author: brasofilo
    Author URI: http://brasofilo.com
*/

/* Trocar de tema conforme a página */
$count = 0;
function change_theme( $template = '' ) {
    global $post,$count;
    if ( is_page('SLUG-DA-PAGINA') ) {
        if($count==0) {
            $template = 'twentyeleven';
            $count++;
        }
    }
    return $template;
}
add_filter('template', 'change_theme');
add_filter('option_template', 'change_theme');
add_filter('option_stylesheet', 'change_theme');