Arbitrarily setting From: header in Mutt

[csj <csj@mindgate.net>]

This is partly a test of my spanking new Mutt installation. So excuse me if
some things like mail wrap fails.

My question: how do I arbitrarily set the From: header in Mutt. I know about
stuff like my_hdr and /etc/email-addresses. What I want to know is if
there's a way to do it so I don't have to muck with the config files every
time I want to send mail under a different persona, something like an
addressbook for myself.

Let's say I want to send two consecutive emails first as "fooman <fooman@chu.org>"
and then as "chu <chu@fooman.org>".