EU Tax

Hi,
Following the rules of EU, I am organizing an event in Spain, so i would need to apply the tax to all Registrants of that country and 0% to the applicants outside that country.

Someone can explain me how to hack the code??
or at least to give me a clue for doing it in the easier way?

thanks in advance

Would creating a custom, conditional fee field work (VAT, set to a % fee), linked to another field (eg COUNTRY) that, when set to your target country(ies) causes the custom VAT field to activate and apply the charge?