Macro to fix aggregate values

I have two Key figure (KF1 & KF2). I have to copy values of KFI to KF2 . KF2 should be editable at details level (e.g Product P1,P2,P3) but the total of these i.e KF2 should not change from values of KF1.

Any suggestions how to do it.

Regards

Shads