How to initialize contract value on SOCO second screen

Hello,

I have a problem concerning the data of the sourcing cockpit : I want to initialize the contract value on the second screen according to specifical rules.

Does a BADI exist to modify the contract value ?

If there is no BADI how can I modify the Webdynpro /SAPSRM/WDC_DO_SOCO_GAF_2 to change contract value at the first screen call ?

I am working on SRM 7.0.

Thank to all.