Item category LIPS-PSTYV as input enabled in VL01n / VL02n

Hi,

When I am creating delivery with reference to order, Item category (LIPS-PSTYV) is coming in read only mode in VL01n / VL02n.

I want make it input enabled.

Pl. guide me user-exit / BADI where I can make it editable on screen.

Thanks,

Maharshi Vyas