Mass change of VAT field.

Mass change of VAT field.

The Dutch VAT% has been changed from 19% to 21%; we need to change this fact in Zoho Invoice so that our items contain the correct VAT%.

Unfortunately, by changing the VAT% in the (browser based) Zoho-sheet, the info isn't translated to the separate items. 
It's also not possible to "hard reset" the items and import the .csv-sheet from the browser based Zoho-excel doc, because Zoho Invoice will not allow us to delete all our items. 

Who can help us to mass change the VAT%?

Thanks!