WB21 ,WB22 Screen Exit

Hi All ,

I have to enhance the standard transaction in WB21(creation of trading contract).At item level ,i have to add a custom field in the ADDITIONAL DATA B tab.whats the approach to find the screen exit or a badi that would cater my requirement or do you knw any exit which helps me ??

I was searching for a SAP proivided screen where we can modify the layout ,as in how we do in case of VA01 or VA23 ...screen 8459

Pls give your opinions ???

Thanks .