I had this setup
bone
attachment1
attachment2
attachment3
skin placeholder
attachment1
This is allowed in the tree, but not in Find and Replace.
I was using this setup for the mix-and-match use case.
skin placeholder is used at runtime. A skin mixer-matcher-code thing looks up and attaches attachment1/2/3 at runtime depending on... you know.. if I have a level 3 tunic equipped. XD
I was using attachment1 under the skin placeholder so I could see what I was animating. Though the truth is, I don't really need to have anything under skinplaceholder in the exported data since my skinning code takes care of it. But that would mean I need to re-add every temporary attachment to every skin placeholder every time I need to make edits.
By the way, I implemented paths for my unity-ffd fork. I gained a tiny bit of exp with using the deserialized json again. XD