Renaming wp_list_pages class

Working solution:

/* Call using: [top_main_menu] */
add_shortcode( 'top_main_menu', 'echo_top_main_menu' );
function echo_top_main_menu() {

    $lookfor = array('page_item');
    $replacewith = array('uk-hidden-small');

    $args = array(
    'exclude' => '134,115,104',
    'echo'          => 0,
    'sort_column'   => 'menu_order',
    'title_li'      => __('')
    );

    $output = wp_list_pages( $args ); 

    echo str_replace($lookfor,$replacewith,$output);
}