I have a question about a sales invoice I need to reverse.

The situation is as follows:

In our system we use sales invoices that update stock, I have a duplicate invoice for a customer that was entered by mistake and I need to reverse it.
Normally I would simply create a credit note for this invoice with today's date and the update stock checkbox ticked and this would successfully reverse the entire invoice.
The problem is, this invoice is in my previous financial year, it was entered by mistake after my accounts had already been sent to the accountant and signed off on. This means I have a balance on my sales ledger accounts that do not match my filed accounts for the year.

Obviously I could always do a credit note for this invoice and change the date to the last financial year, However I believe it is not recommended to process a stock transaction with a date prior to today's date, is this correct?
If so, what is the best way to reverse this transaction so my accounts in Hansa Match my filed accounts with my accountant?

Many thanks