We had a requisition which was created for $0. And this requisition was approved and then autocreated to a Standard PO which also was $0. The PO was approved and then the dollar amount was changed and then again submitted for approval.
Is there a way to avoid/prevent the PO from being modified after it is autocreated from a requisition and then approved?
As far as I know for a given PO it can be modified by the user as long as he has all the security prieveleges or is in the approval hierarchy.
One thing that can be done is that you can check in PO_DISTRIBUTIONS_ALL whether this PO has been autocreated. Autocreated PO would have a req_distribution_id populated in the PO_DISTRIBUTIONS_ALL table.
And if thats the case then open the form in Read-Only mode.
Std Purchasing Application opens the Consumption Advice PO in read-only mode. So you can look at the related code as to how it was achieved.