Hi @elbastion:
The invoice is not updated after issuing a refund because we follow GAAP (Generally Accepted Accounting Principles) which means that administrative changes should be documented separately. This means that an original invoice should never be modified by a refund. In most countries (at least in the EU) this is even considered fraudulent (and illegal). We have chosen to follow this in both the free and the paid extension.
That said, the Professional extension includes 3 new documents: the proforma invoice, the receipt and the credit note. The last one will allow you to create credit notes to your full or partially refunded orders.
See: Creating a refund / credit note.
Please note that the forums rules does not allow us to provide premium support or answering pre-sale questions for paid plugins here, therefore, please contact us at [email protected], if you have more questions regarding the Professional extension.