I find it is quite common to start impala-shell with the --quiet option, then within the same session want to turn on the extra output like the timing numbers. Or to start with the normal ASCII boxes for query output, then want to switch to comma-delimited output. Currently, this involves quitting out of the shell and restarting it, plus doing an extra USE or -d to get back to the same database as before.
I suggest having some command in the shell to switch between quiet and verbose mode, boxed and delimited output, and set the delimiter character. Perhaps there are other similar command-line settings that would be easy to toggle while the interpreter is running.