Registration - making 2 fields exclude each other

Hello, I hope i won't annoy too much with my question

I need to modify my hikashop registration form so that if the customer is a single person, the " tax code " field is required and there is no " vat code ". And if the customer is a company, the " vat code " is required and there is no " tax code ".

With " tax code " i mean the personal fiscal code that every person has, and with " vat code " i mean the code that each company has.

How may i do what I explained ?

Thanks in advance for your kind disposal