This piece of code should do it for you. Place this code in your theme’s functions.php file. You can add customizations to the custom_password_form() function – just don’t use print or echo – the function must return a value.
ID ) ? rand() : $post->ID );
$o = '
';
return $o;
}
?>
this is the solution from :http://wordpress.org/support/topic/how-do-i-change-password-protected-text