VAT ID number on previous invoices

It is possible to re-issue invoices with the new VAT number. However, note that this process might not be super straight-forward. That's mostly because editing/changing tax-related information on any official documents (such as invoices) might have serious implications if the right process is not followed.

First thing you should do - open a support case from your account (if you have only one account - then open it from there... if you have Organization with multile accounts, then open a case from the Management Payer root account). Choose the billing category - the case will go to the relevant customer service team to handle your request.

Generally, (on a high level) support team would have to "cancel" your old invoices. And then re-creating those invoices (with the same original cost) with the new invoice ID, but including your new VAT number.

Though, it's possible that the total bill might differ from your original invoice, in case you had wrong address in the wrong country, and without a tax number set up on the account... If you updated correct VAT number, then the amount of tax that was originally charged on the invoice in this example might be different from the amount of tax you'll have on your updated invoice (the billing system wouldn't know that the tax charges are incorrect, if the account settings such as billing address are incorrect).