Changing client details shouldn't change your invoices retrospectively, that would create quite a mess in your documents.
If you need to change the client's details on an invoice, proceed as follows:
- In the Client's list edit the client and change its details
- Edit the invoice and select another client (any client will do)
- Save the invoice
- Edit the invoice again
- Select the right client
- Save again
Now the actual data from the client has been refreshed in the invoice, and you will see the desired client's details.