How to mass update the Tax Regime Code in customers?

Summary:

I am trying to massively update a list of customers in order to include a country level tax registration number (not tax regime tax registration number) as it is needed to comply with customers process. When trying to use the FBDI template to do this update I found that the country level tax registration number is not available as one of the fields in the template.

I have attached a screen capture of the field that I need to update, could you help me with a method to do this update in batch for multiple customers or which field of the template I should be using.