At the moment Shopify does not allow making changes to the original order once it has been paid and fulfilled.
Generally there are two approaches we see merchants engage in to process exchange orders:
Refund the customer for the item(s) on the original order
Then create a Draft Exchange-Order from the Rich Returns' dashboard with the full item-price and send the invoice to the customer
Create an Exchange-Order from the Rich-Returns dashboard with item prices set to $0 in the settings
What some merchants are trying to forcefully achieve is to make changes to the original order so that their Sales Statistics stay the same: 1 order, same order value. This sugarcoats what is really happening in terms of cost and attribution:
Suppose you have an order of 2 items with each item at $50 ($100 total)
The customer then wants to exchange one item in the order
The first instinct is to make changes to the original order so it stays 1 order and AOV is $100 looking at only this order
The reality is that you needed to fulfill 2 orders, so 2x the cost associated with an order to really make the sale
If you take a look at the "Longer Process" above or at return process of large eCommerce merchants like Zalando they only have two product-flows: IN and OUT
In these cases the customer needs to
return 1 item
then place a new order for a different size
Result is the same: 2 orders, $50 AOV
Especially if employees are compensated purely on these "acquisition metrics" it is important to set up compensation with customer returns in mind.