On posts going back to 2003 I red it was possible to switch identity
while composing a message. What I understood from those posts was that
you had to put the following lines in .muttrc:
------------
macro compose z "<edit-from>^UIdentity_<tab>" "Select from"
alias Identity_1 <1st_address@xxxxxx>
alias Identity_2 <2nd_address@xxxxxx>
..... .......... ....................
alias Identity_n <nth_addressi@xxxxxx>
------------
then, pressing 'z' while editing a new mail, you would be able to change
your 'From:' header choosing from the list of identities. However, I did
try it with no success ;-(