Not able to remove Default tax regime code

Hi,

When i create invoice for vendor default tax regime code is appearing at tax lines summary form with some tax rate. I would like to remove this tax lines but it's grayed out and not able to change Regime code.

Actually i have two Regime codes i.e. UK & FR. Default regime code as UK for this invoice but i would like to change from UK to FR it's not allowing. How this regime code will default?

I would like to attach default FR(regime code) only for this supplier. How to do?

Regards,

Madhu