Independent Requirement Variant Configuration to Purchase Requisition During MRP

During an MRP run we would like to copy some of the characteristics from the variant configuration of an Independent Requirement to the Purchase Requisition.
Can anyone suggest which exit/BAdi I can use to do this.

And how can I select which characteristics I want to copy.

eg. In MD83 I can see the variant configuration against item 10. There are 20 characteristics. When MRP is run I want to copy 5 of them to the Purchase Requisition which is created off the back of that document item.