How to apply offset tax on AGIS created invoices - in Upgrade Mode

Client has upgraded to R12.1.1 with STCC Mode with regards to Tax (as we have 42 Operating units, too much time for now to migrade to Tax Determine Regime.

We are using AGIS for Intercompany Invoices, where we can have a Portuguese Company (using P0, or P 0 intra eu tax rate on the AR Invoice) invoicing a Swiss company. The AP Invoice should have Swiss Offset Tax.

Correct tax rates (tax classification codes) are set at customer and supplier level.

However as we are in STCC Mode, the AP invoice has to have the same tax rate --> P 0. If this does not exist, the AP invoice cannot even be validated, nor changed to another tax rate.