The motivation for this idea is, to give users in a global organization the ability to run in the system a yearly VAT declaration that is based on prior advanced monthly / quarterly declarations out of the box.

This includes giving the flexibility to change/ correct the declaration prior submitting the declaration (recommended only to allow this functionality for yearly declarations) to reduce on the one hand manual efforts and on the other hand to ensure consistency in the system E2E for all VAT transactions and declarations = system as single point of truth, no 3rd party (tool) is required.

The approach of generating the declaration should therefore be in the same way as already implemented in Intrastat https://docs.microsoft.com/en-us/dynamics365/finance/localizations/tasks/transfer-transactions-intrastat and Italian localization modello 770 https://docs.microsoft.com/en-us/dynamics365/finance/localizations/emea-ita-modello770 consisting of the following steps:
Copy all original transactions (posted sales tax transactions) into a new data entity
By using the copied data, in an interface a user can review the data and correct/ add transactions if required to fulfill especially annual declaration purposes
The declaration using Generic Electronic Reporting uses instead of „posted sales tax transaction“ table the NEW one and generate the file in the country specific format based on reporting codes.