VA42 user exit to update contract start and end dates at Item level

Question

Hi  Experts,
                  I need to update contract start and end dates at Item level in 'VA42' transaction, for this i am using user-exit 'USEREXIT_FIELD_MODIFICATION' in the include 'MV45AFZZ'. i am able  to display the data into item level through my coding but the data is not getting updated into 'VEDA'
Note: No need to change contract start date and end date in header level. Only at item level i want to change dates.
Thanks,
Sateesh.

Answer 1

Thanks For your reply Vikram,
      i tried with 'USEREXIT_MOVE_FIELD_TO_VBAP' user-exit earlier it self its not working. Can you suggest me any another way how we can achieve this functionality. modification of Contract start date and end date in only item level. 
'USEREXIT_MOVE_FIELD_TO_VBAP':
FORM USEREXIT_MOVE_FIELD_TO_VBAP.
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""$"$\SE:(3) Form USEREXIT_MOVE_FIELD_TO_VBAP, Start                                                                                                           A
*$*$-Start: (3)---------------------------------------------------------------------------------$*$*
ENHANCEMENT 1  ZSD_CONT_DATE.    "active version
DATA : lv_var TYPE CHAR10.
  lv_var = '0040000219'.
  if sy-tcode = 'VA42'.
IF VBAK-VBELN EQ lv_var.
VEDA-VBEGDAT = '20140502'.
  XVEDA-UPDKZ = 'X'.
VEDA-VENDDAT = '20140602'.
  XVEDA-UPDKZ = 'X'.
ENDIF.
ENDIF.
ENDENHANCEMENT.