If you're verifying an option you need to return true or false. False would throw an error. True wouldn't error, but also it would save the changes.
I'm unsure if there'd be a way of reverting back to the original value... I guess it would be something like:
PHP:
$dw->set('option_value', $dw->getExisting('option_value'));
return true;
Though, really, I haven't tested it (or given it much thought

) so proceed with caution
EDIT: Probably worth noting that silently not changing an option like this is probably quite an unexpected behaviour for an end user to experience so it's not ideal... are you sure you need to approach it like that?