/server -m ircserveraddress port -i nick altnick

ive just read this code in mirc help. u can use this in auto joinning script, so before connecting new server it opens new status window and changes nick and altnick.
Code:
/server [-mnsar] <server/groupname> [port] [password] [-i nick anick email name] [-j #channel pass]

is it what u need or not?