Customer exit for tab 'Billing Plan' at item level in VA02

Hi gurus,

is there any customer or user exit for tab 'billing plan' in va02 where we find other tab like SALE A, SALES B, SHIPPING etc, i allready tried mv45afzz (userexit_field_modification) and exit V60F0001( Cmod). the requirement is to suppress field NET VALUE for certain user n based upon sale order type. so i cant use transaction variant.

well i found one include "RV60FUS4" which contain form 'userexit_field_modification' but i dont know how to change the code n through which user exit.

any reply will be awarded.

thanks