I needed to edit the "invalid promo code" error as it is a valid code, it's just they need to be logged in to use it. Since our login (within the cart) is designed on the next page, it really wasn't working out wording wise.
$this->__('Coupon code "%s" is not valid.', Mage::helper('core')->escapeHtml($couponCode))
$this->__('This coupon code "%s" can not be applied now or it may require you to <b>login or register an account</b> to use it.', Mage::helper('core')->escapeHtml($couponCode))
However: is that safe for future upgrades? And how do I make "login" and "register" links? After I added the html the page went white so I had to just bold those words for now.