There are many transmutes in the game and with the appearance system being updated I believe this would be a nice feature to add into the game for collectors.
Back before the appearance system changes you would have to delete old appearances to use new ones which would cause a problem with not being able to use the old appearances.
The Main Idea I have here is to add a way to receive your old appearance items such as pulling them out of collections. For example, I have Sinister Spear in my collections and used as appearance back when it was out and overrode it with another appearance. I now don't have the sinister spear and it's not like I can obtain it anymore. So having a feature like pulling out transmutes from collections would be amazing.
With a feature like this you could make it so it only works with transmutes so people won't abuse the feature to get gear for other characters for free.
Here's an example of a transmute that I had which I can't use because of the old system: