Copy value to several lines

Hi Guru's

I need to do a BPS function to copy the value from a line to several lines (already existing):

source Line :

contract : #

Type : MOY

Average : 12

Familly : 1772

Target line :

COntract : 2100089

Type : CT

Average --> Should be 12

Familly : 1772

COntract : 2100078

Type : CT

Average --> Should be 12

Familly : 1772

the common key is the familly. and the different key is the contract.

How can i manage this in BPS.

Thanks for help.

Cyril.