What is the best possible solution regarding purchase orders if VAT is being implemented?

Hi Team,

We recently had Middle East VAT implementation in our project. Some of the areas where inputs are required , are:-

1)How to deal with update of tax rate area and explanation codes in existing purchase orders?

What we did => We asked the client to provide list of open POs (stock + non-stock) i.e. where NEXT status <> 999 and updated the tax area , explanation code in F4301 by SQL and tax area , explanation code and taxable (Y/N) = Y in F4311 by SQL.

2)Now , the issue is related to those orders for which entries in F43121 have already been made i.e. partially received and vouchered , partially received but  not vouchered and partially received and partially vouchered.