update Billing plan in VA01 / VA02 / VA03 with items restriction.

Hi all,

I have to update Billing plan in VA01 / VA02 / VA03 with below restriction.

Restriction base on Item no.

1) Sales order having more then 0020 line items then its should not consider in Billing plan but it should calculate in Net price.

please suggest me .

any BAPI / BADI or User exit for this requirement .