CO11N,Restrict modify consume material QTY

Hi gurus,
In our company,all material used as backflush material. So when do CO11N, the material consumed automaticallly. In fact, when do Co11N, user can modify the consume mateiral QTY more or less. We want to restrict user to modify the QTY, and only one range he can modify, for example:
finish goods QTY(confirmed qty): 100 EA
one consumed material(say B) QTY: 206 EA ( 3% come from BOM master data)
We want to restrict user modify B material base on QTY beteween 200 and 206 EA.
Is there solution can match this requisition? User exit or config or other solution?
Thanks a lot!


Hi Daniel,
You can refer to the following user exit. one of it will work. Just check these:
CONFPI01            Process order conf.: Calculate cust.specific default values  
CONFPI02            Process order confirmation: Customer spec. input checks 1    
CONFPI03            Process order conf.: Cust. spec. check after op. selection   
CONFPI04            Process order conf.: Customer specific input checks 2        
CONFPI05            Process order conf.: Cust. spec. enhancements when saving    
CONFPP03            PP order conf.: Cust. specific check after op. selection   
Hope it helps...