Want to update an invoice after it has been validated but not paid.

I just want to confirm what I believe I have read.  Once we validate and invoice, you can not update the invoice date or amount, even if it has not been paid.  The only way to do this would be to check the Allow Adjustments to Paid Invoices.  Is this true?

My client on occasion would like to update the invoice after it has been validated but before it is paid, but can not.  Field such as invoice date, invoice amount, etc.