A list-owner can not add or change another's LISTSERV password.
A list-owner (who remembers their own password) CAN update the
list's password:
 
1) GET listname (NOL HEAD
 
2) receive file
 
3) update headers in the file with list definition keyword
 
   * PW= new_pass_wod
 
4) send the file back to: LISTSERV with the appropriate
   prepended PUT command that specifies the OLD list password
   or the list-owner's current personal password
 
PUT listname LIST PW=old_pass_wd
... rest of headers (no signature block)
 
5) pray.