You can use the node view to preview the usd file and simply edit the usd file, such as overriding prim, switching variants, adding references or payloads, and modifying attributes.
usdtweak is a free and open source editor for Pixar's USD format. usdtweak can already be used for small and simple tasks like cleaning assets, creating and editing layers, inspecting and fixing usd stages. It works on windows, macos and linux.
TinkerUsd is an experimental project written in C++ for R&D purposes. This project is free and very much work in progress.
