How to user MOH concept for Existing item to be Received through PO

Dears,

We have below requirement to acheive:

1. We have around 40000 items in our organization which is non-OPM and OPM items and we are using 12.1.3 average costing
2. We need to know how to add freight charges, additional charges to item cost. We dont have advance pricing and LCM in our environment
3. When we check for MOH setup for adding fixed percentage cost for PO transaction, it is not updating the existing items' po transactions.
4. How to add it automatically for the existing items PO transactions without manual. System should consider the MOH absorption rule for existing item than new items. If can please provide steps to do same.