I've got a couple of customfields which are visable in the front and, obviously, display as input textboxes however need these to be textareas rather. Can you really change how customfields output? If what exactly would I have to do in order to get this to change?

please find out more about

get_publish_meta (to show your meta_data from the publish) http://codex.wordpress.org/Function_Reference/get_post_meta

update_publish_meta (to improve your meta data from the publish) http://codex.wordpress.org/Function_Reference/update_post_meta

isset (to possess your submission button to update_publish_meta(must be on the top from the page)) http://php.net/manual/en/function.isset.php