Hi,
Choosing the skin placeholder which you want to put in a new slot and drag and drop it outside of the slot can separate the slot. When you drop the skin placeholder, Set Parent dialogue appears and you can set the new slot name. Alternatively, you can do it by creating a new slot clicking the New... button in the tree property, then using the Set Parent button and then clicking the new parent(slot).
By the way, if you have a question about how to do something in the Spine editor, please post your question in the Editor category. http://en.esotericsoftware.com/forum/viewforum.php?f=11
