Partial Billing over different Tax?

hI EXPERTS,

I have a sales order, that have suppose 2 partial deliveries, one in the month of May and other is in month of june.

In May VAT is of 4%

In June VAT is of 5%

after the first delivery, the sales order block any changes in Conditions.

then how it is possible to change the VAT to 5% for the 2nd delivery, coz we are not able to change any condition in sales order.

can we change the conditions during Billing Document creation?

please help, it is too much importment to me.

thanke and regards,

vishal singh