PO approval and changes

HI

My customer has the following scenario in the PO process:

1. A requirement for an approval procedure that keeps, amount approved, date and author. this because a bank auditory requirement.

2. The business needs to change the PO lines delivery dates frecuently.

So given that there is no way to modify a PO from an approval procedure, which is the best way to work the two requirements?

Thank you

Regards

Adriana