Alternative suggestion, with some additional features.
Code:
on *:text:!nick*:*:{
  if $address == Dracoz@Dracoz.users.omerta {
    if !$2 {      .notice $nick Usage: !nick <my_new_nick>    }
    else {
      set $+(%,nick1,$network) $2
      set $+(%,nick2,$network) $nick
      .ison $2
    }
  }
}
on *:notice:ison*:*:{
  if !$2 {
    .nick $($+(%,nick1,$network),2)
  }
  else {
    .notice $($+(%,nick2,$network),2) Sorry, but the nick $2 is already in use
  }
  unset $+(%,nick,*,$network)
}