Change Profiles for PO and RO
You can set up the changeability of PO is for a given status in SPRO.
To do it got to:
Supply Network Collaboration->
Make General Settings for Purchase Orders
Here you can find the setup for the change profiles, if the Display only flag is set, you can’t change the PO in the given status combination.
You can check the exact status combination of a PO on the PO detail screen.