I would say it depends on what you’re trying to do. E.g., you can change/add attributes in the front end via the States page, but that is temporary. As soon as the entity updates itself, those changes will likely be gone.
You say you’ve saved the level of a light. Are you looking to restore the level of the light back to that saved value? If so, then you should use the light.turn_on service and specify brightness.
I guess it would be easier to help if you were a little bit clearer on what you’re trying to do.
FWIW, you might want to check out this python_script I made (which just happens to save and restore switch and light settings 
):