Tradesolution EPD handles discontinuing in another way than GS1. You need to withdraw the product hierarchy and then D8324 "NedlagtDato" will be set automatically to tomorrows date as part of the withdrawal. Every unit in the hierarchy is marked withdrawn (unless a unit still has another active top parent).
You can not set D8324 (it's read only).
If you want to schedule a withdrawal in the future, then set X9000 to Y for all product units in the hierarchy and set X9001 to the date in the future on the pallet.