No built in way, but there is nothing preventing you from writing your plugin to use a config file instead of settings stored in the database. When your nodebb starts instead of loading your plugin settings from the database you would read it from the file.

/api/categories doesn't load the data via sockets, you can check it on this forum, just check the network tab and you should see the loaded categories.

Great . Exactly what I needed. Just couldn't find it in the documentation.