Item Category determination for substitution's sub item

Hi Experts,

I have an issue in Sales order while determining item category for substitution items. Could you please help me? Below are details.

When user entered an item which has a substitution material, has rightly determined item category. Defaulted correct sub item's item category based on "Higher level Item category".

When user changed the parent item's item category to a standard item category (Eg. TAN). As per SAP standard, the sub item category should be re-determined based on changed Higher Level Item category, but it didn't happen.

Due to this, the parent item is delivered and billed, but sub item cannot be delivered without parent item. We couldn't edit this sub item and reject.

I wanted your help in either re-determine the sub item's item category or for rejecting this item at sales order.

Thanks in advance.

Regards,
Joshua