Use the Asset Editor to modify an asset without changing its assignment to a material. Use the Asset Browser in conjunction with the Asset Editor to edit material assets.
Any asset in the Document Assets collection can be edited. Assets selected from libraries will be loaded into the project for editing.
To edit an asset
Settings panel
Additional Settings drop-down
Material Assets.
The Asset Editor opens with no loaded assets.
(Opens/Closes Asset Browser).
The Asset Browser opens.

In the asset list, the
icon indicates legacy appearance assets. For details, see
About Appearance Assets.
icon) for materials. This practice ensures that views and rendered images use the most up-to-date, highest quality representations of materials.
Assets are saved in a Revit project or in a library. Assets that are in a Revit project but are not referenced by any material are saved to the Unreferenced Assets library. You can create and edit unreferenced assets during a Revit session as needed. However, you must save your Revit project in order to save any unreferenced assets created or edited during the session.
You can also save unreferenced assets to the user library, Favorites. In the Asset Browser, right-click an asset in the Unreferenced Assets library and click Add to
Favorites.