Updating material characteristics at header level for entire material doc

Dear All,

We have a requirement, while doing GR we will have a max of 50 line items all for one single PO and the material will be having one characteristic "Country or Origin"

My user need to enter this characteristic at the header level since it came from one single vendor...if he updates it in header level it should be copied to all the line items.

Please guide me how to proceed.