Change item category in delivery order

Hi everyone

Issue: Can not change item category in delivery order.

Phenomenon:

1:Create purchase order and receive item based on it. complete invoice verification.

2:Use MIGO to create return delivery based on material document that is created during above process.

3:Based on system settings, (Sales org, ship-to party etc), outbound delivery is automatically created in background.

4:Try to change item category which is already determined during delivery order creation, but it is grayed out.

Can we change item category in this situation?

I have checked thread "number-of-attempts-to-change-item-category

This looks same issue but I still do not know how to control item category in delivery order.

In material type, is there any place I can configure to allow user to change item category

in delivery order?

Please advise.

Satoru