How to add a SAVE button to replace PUBLISH on a custom post type?

Not mine but modified from here.
But if you pop this into functions.php or a plugin it will work.

add_filter( 'gettext', 'change_publish_button', 10, 2 );

function change_publish_button( $translation, $text ) {
if ( 'yourcustomposttype' == get_post_type())
if ( $text == 'Publish' )
    return 'Save';

return $translation;
}