Hi Narasimha,
Easy way is to create another cube (say IC1) and pick the wrong set of records from Original Cube and load into IC1. While loading from IC1 to original, create two rule groups one for reversal of existing records (i.e., multiply all KeyFigures with -1). In another rule group load right value of KeyFigures.
Another is similar approach but self loop, means read data from Original Cube and load into same with new KF value and Reversing Original KF.
Hope it gives idea!
Thanks,
Umashankar