Creating an invoice means creating a serie of stock-lines (product/quantity/value) and simple-lines items (value) These lines are associated to a partner.

You should consider validating the invoice when you send it to your partner. That way, the partner address and contact will not change anymore for this invoice, even if your contact and/or partner address change for forthcoming invoices.

Moreover, the accounting movment associated will not be modifiable anymore from the accounting module. The drawback is that you can not anymore modify the invoice. But if you have sent it yet...

The associated order is then automatically validated too.