unique skin tranfer.

does it work, from unique to non unique item?
(of same type, details? armor to armor, ES to ES, etc? or it works with hybrid EV/ES to ES, ? )

I am not sure about the limitations of the skin Transfer, but in POE 2, I was able to use it to make my yellow body armor (it was either full ES or Armor/ES, I don't remember) look like the Prayers of Rain (unique).

I also want to mention that when I used the skin transfer and clicked on the Prayers of Rain unique in order to save its appearance, it caused the Prayers of Rain unique to disappear. So, I'm not sure if this answers your question. But I just thought I would add in my experience using the skin transfer.