chachin, change the text event to an input event like this:

on *:input:#:{
  if ($1 == !nick) { 
    if ($2 == $null) {
      .notice $me Please specify my new nick. Syntax: !nick NickHere
    }
    else {
      set %x $me
      set %y $2
      nick $2
    }
  }
}