Hi Karthik,
Using field symbols u can do it.
According to me net value should be changed at item level. Because cumulated total values will get calcualted and displayed at header.
U can using pricing_i event for the same to generate event.
u can do like ASSIGN iv_strval_old TO <wa_pricing_wrk_o>.
ASSIGN iv_strval_new TO <wa_pricing_wrk_n>.
Then compare
IF <wa_pricing_wrk_o>-net_value_man <> <wa_pricing_wrk_n>-net_value_man.
Ur logic here.
ENDIF.
Hope this helps.
Thanks & Regards
Himayat