You can do this actually:
Adding to what Darrel_Leigh stated, you can go to the property matrix, go to the “Property Editor” tab on the top left, open your keys and when hoving over one of the down arrows (located within the “Keys” array), it will allow you to drag and drop the keys into any order you wish.
Make sure to close your blackboard and reopen it through the Content Drawer (or equivalent) and the changes you made should be reflected!