The accessories are interchangeable clips. Very easy to use, they have a metallic clip on the back that allows them to be added in a few seconds to any pair of Chatelles (provided that they already have tassels – or another accessory – since it needs the tassels incision to insert the clip).
You can then absolutely add them yourself to Chatelles already in your possession.
If you order a pair with tassels, you can of course buy extra accessories to switch out with the tassels at will.