Delivery item category

Hi SAP Gurus,

I have some problem with delivery item category determiantion. We have Item category ZISP and now i have created another item category ZSTO. When ever i try to make an item category determination for delivery for ZSTO its saying that the entry already exists. Because both ZISP and ZSTO is been copied from TAN. So already an entry is there like ZLF-NORM-NIL-NIL-ZISP. So is there any way i want to add ZLF-NORM-NIL-NIL-ZSTO.

Plse help me out

Rewards will be given

Thanks

Edie