In an approved project we have the ability to assign a new item to a change order, or to use the right-click context menu to reassign it to a different change order. However, items being deleted cannot be reassigned to be deleted via a different change order - my workaround is to undelete them, and then re-delete them against a different change order.
I would even call this a bug in the case when the deleted items are replaced by new change order items. Reassigning the new item to a new change order should also automatically reassign the replaced item to that same change order. Please advise if this specific issue should be submitted as a bug report.