Add a custom text to admin footer in a Custom Post Type page

This should do. Put the following in your functions.php

if (in_array($GLOBALS['pagenow'], array('edit.php', 'post.php', 'post-new.php')))
    add_filter('admin_footer_text', 'my_custom_footer_admin_text');

function my_custom_footer_admin_text($text) {
    $post_type = filter_input(INPUT_GET, 'post_type');
    if (! $post_type)
        $post_type = get_post_type(filter_input(INPUT_GET, 'post'));

    if ('my_post_type' == $post_type)
        return 'my custom message';

    return $text;
}