I wouldn't say it is "impossible", depending upon your shell programming expertise (are you good with perl?) but it is not really feasible (it would be a lot quicker to do it in the Control Panel).
There are no shell commands (scripts) for doing any of that that we users can get at, and there is no published API, so any "hack" you make to do it is likely to break with a future panel change/modification (and it is being "tweaked" regularly).
There has been some "proof of concept" work done automating some Control Panel functions using PHP scripts and cURL. Last time I checked there is "working" code showing how to add a new email forwarding address, and for creating a new subdomain - other stuff could ostensibly be done the same way.
The problem is that, since it is "unofficial" and there is no API, I don't think anyone has been real interested in doing a bunch of work on it that could be rendered useless with a new Control Panel code release.
What information I know of can be found in this previous forum thread.