Hi Pilvi,
Aside from /SAPAPO/CURTO_EDIT, you can use MASSD to update Procurement Priority in mass in SCM 7.13.
During order creation, the sources of supply are ranked as described in SAP Help. This way, the source with highest priority will be chosen first.
Please, notice that if the PDS with highest priority cannot cover a demand on time, the planning function (heuristic) may switch to a different source of supply, that has lower priority but that can cover the demand on time.
Regards,
Tiago