You can add a status “Exchanged” to Web. But it won’t do anything in WooPOS. If you change status to “Cancelled” or “Refunded”, the stock will be added back to QOH.

To do an exchange, you have to create a new invoice in WooPOS, sell original items with negative quantity (or use Return function), and sell new items with positive quantity. You can do the same thing on the web, or modify the order on the web, but all changes (except order status) will not be synchronized back to WooPOS.