There is a setsave() method for all classes, but this wouldn't even be needed if set() and save() were chainable. Neither have a return, so they're just returning None. There may be other places where this would make a difference. Just return self to allow:

settings = load_json_settings(myfile, {'mykey': 'myvalue'})
settings.set('this', 'that').save()

It was just a thought. setsave() probably wouldn't exist if I had considered this earlier (I usually do, but this project is kinda old).