Here is the Asset Editor in form of Unity project: link Alternatively, you can get a 30 days trial if you like, and you can renew it by simply creating a new account every time (no credit card required I've been told).
To use it, you need 4.6.1p2 and it has to be Pro in order to save your changes (use torrents, there is a patch that works on all Unity versions). It's supposed to allow you to edit/replace variables, meshes, sounds, textures, particles, shaders, animations, and maybe some other things that I can't think of right now. You can import stuff in though, so you're all set. Can't extract things out yet (but you can do that with Disunity). This is a Unity Editor Extension which allows Unity to work with.
