Some things are simply impossible - however, it's useful to say why not (or better yet, how it could be done, but how incredibly difficult it is).
If we had a question like
I need to alter my turbo enfrobulator using the degobulation widget on frobster 2.0 - how do I do this?
You can say
Or you can explain that you can't enfrobulate from the degobulation widget - it only handles degobulation related settings - you need to do so using the enfrobulation command line tool.
The former dosen'tdoesn't help. The latter does. If you need to say it isn't possible - it's useful to say why it isn't possible.