You don’t need to change the line… you can just add the following line and it will filter the content as well as the excerpt:
add_filter(‘the_excerpt’, ‘print_wp_cart_button_new’,11);
To display a button on the sidebar use the following PHP function (you can pass in the product name and price to the function):
<?php echo print_wp_cart_button_for_product(“PRODUCT-NAME”, “PRODUCT-PRICE”); ?>