Yes, carving in cement is possible. You would want to use a different recipe for that though - no peat or perlite, more and finer sand. You'd probably want to start with more of a columnar shape rather than a bowl shape. It needs to be carved when quite wet yet - after only a few hours. I've never done carving myself but have seen lots of beautiful work.
You could also use a mask as a mold. Just be sure to put plenty of Pam on it so the cement releases.