Set that up in on CONNECT or else use -i with /server...

/server -m irc.network.com -i nick

If you want, you can even set your own alias that will do that for you...

Code:
myserver {
  var %nick = defaultnick
  if (irc.network.net isin $1-) { var %nick = nick }
  elseif (irc.network2.net isin $1-) { var %nick = nick2 }
  elseif (irc.network3.net isin $1-) { var %nick = nick3 }
  server $1- -i %nick
}


That's just a quick example of one way you can do that. There are a variety of ways to handle the situation and they'll depend on exactly what you want to have happen, such as whether or not you are using different nicks on many different servers or just a couple.

Invision Support
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