We’ve added the ability to add, remove, or update discounts to existing line items when editing orders. Previously, discounts could only be added to new items, and couldn't be updated or removed.
This gives you more flexibility in how to meet customer expectations and improve customer retention. For example, this allows you to retroactively apply missing discounts if customers forget to do so at checkout.
Note that only manually added discounts, such as those applied through editing or draft orders, can be updated or removed.
For more information about editing with discounts, visit our Shopify Help Center.