user exit in CJ02

Hi experts

i am need of some exit like in CJ02 when the user status is some ZXXX i want to disable the whole fields and should not allow the user to change the status in that screen

the screen details are as follows

cj02->enter the wbs and client details ->press enter->in basic data table below there is a blue color 'i' icon will be there , there we can see the status and we can add upto n number of status there

so if the status is some zXXX then i want to disable all the fields

Any pointers on this are welcome

please throw light on this

Thanks and Regards

S.Janagar