Can't save changes to an item? If an item has been used in a transaction, you can't change its inventory settings (such as selecting I track stock for this item to turn on stock tracking), but you can duplicate the item – see Updating items to use stock tracking.
When you're done, click:
Save to save your changes.
Save and duplicate to save your changes and create another item with the same details and a new Item ID. You can then customise the duplicated item.
Save and create new to save your changes and create a new blank item.