Is there a way I can set a customer to be VAT exempt when they register? I would like the customer to be able to check a box in the registration form (I know how to add a field there) and that would make the particular customer be treated as VAT-exempt (e.g. by setting the customer's tax field to 0). I want to be able to do this at time of registration so the customer can go straight to making a purchase and not wait for the store admin to set the tax rate first. At the moment I am thinking of hacking the database access to return a zero value in that field if my extra registration field is set, but that will not be easily maintained when Catalook is updated so might there be a better way?