I have a custom field in my onepage checkout, that is used in a Model\Observer.php
to set the customer group using the following:
$customer = Mage::getSingleton("customer/session")->getCustomer();
$customer->setGroupId($newGroupId)->save();
This all works great, and I'm doing this to change the Tax in the cart.
However, for people checking out as a guest it throws an error:
customer email is required
Is there a way of setting a customer group for a guest, a second NOT LOGGED IN group for example?