Change label of title field for posts in the backend

function change_post_titles() {
    global $post, $title, $action, $current_screen;
    $title = "foo<br>bar";
    $title = str_replace('<br>', ' ', $title);
}
add_action('admin_head', 'change_post_titles');

Use this this will give the result you want. Please check it let me know for any doubts.