Complex PO created with wrong currency and a Work Confirmation exists with 'Processed' status

Dear All

My case is as follow:

Customer create a Complex PO with wrong currency.

Then he created a Work Confirmation to this PO and Approve it

When he wants to create the invoice, he discovered that there is a mistake on the Currency.

As we can't cancel a WC with 'processed' status, I tried to correct the Amount of the WC by inserting '0' and submitted it again I got 'Processing Error' in test environment, I'm not sue that this will allow me to cancel the Complex PO and create it again with the correct currency.

So, do you think by putting the amount of the WC = 0  this will allow canceling the PO?