autoship_product_message_string

The 'autoship_product_message_string' filter which takes the current message and the product id, allowing you to display/customize the Product Message on a global or product level.

function xx_modify_product_message_string($default_msg, $product_id){
    return $default_msg = '<br>Hello World<hr>');
}
add_filter('autoship_product_message_string', 'xx_modify_product_message_string', 10, 2);