Dear KD,
The behaviour you getting is correct to avoid inconsistency.
Delivery costs conditions should not be changed once goods receipt is done for a purchase order item. For this reason once a goods receipt is done, the delivery costs conditions are marked as fixed.
Once you have GR, then this condition should not allow to delete or even change as this will bring you
to inconsistency.
There is no setting for this to allow you change it as it is intended.
Regards,
ian Wong Loke Foong