Customization to Order Entry

Hello, I’ve been asked to add Discount per Item rather than total Discount in Order Entry. I was wanting to just add OrderDtl.OrdBasedPrice to populate a field within Order Entry. However, I’ve been unable to figure out why the Like column cannot be updated. I can create a UD field for this, but if the field already exists in OrderDtl why can I not just add it like any other field in OrderEntry. This is what shows currently. Any help would be greatly appreciated!