Hi Lina,
Its difficult until and unless you decide some cut off date for the existing Pr Org and before creating new you need to make sure that there are no open documents (SC, PO etc..) with the existing Pr Org.
After achieving first step, You can create a Central Pr Org and under it Create Country Node, Comp Code and Pr Grp. In Pr Grp responsibility you can give the Comp code Org id.
Best Regards,
Anil
