I would suggest to both of you to take a look at the List Owner's Manual
which is available from our ftp site, ftp.lsoft.com, in the DOCUMENT
directory.  Alternately you can view the latest version on the Web at
http://www.lsoft.com/manuals/owner/listserv.html.
 
In terms of changing subject lines and body content, you as editor make
those changes, then forward the message back to the list.  It's that
simple.  You should use a mail client that generates "Resent-" header
lines, else the edited posts will appear to be coming from you, but
other than that, that's how it's done.
 
Nathan