You can save any of your creations into your own asset packs. Folder creation/management is also supported, so just Blockbench can manage your entire Common directory!
You're free to open any model/texture into blockbench.
You can run the command `/blockbench` in Hytale to get an authorisation key. Blockbench will have a new panel called the Hytale File Browser which you can connect to Hytale with using the key you obtained.
You'll see all of the asset packs installed on your world, including all of their Common files.