When using the /server command to connect to a server you can use the -i switch to specify a different Full Name. /help /server
As for identd you would have to connect to one server (until mIRC gets the IdentD request) then change your UserID using /identd and connect to the next server. If you wanted to use auto-reconnect then you'd need to handle that aswell. Alternately you could disable mIRC's IdentD server and use a stand-alone IdentD or a socket script that did the same.
