I tested it and it only triggered when the file changed. I wonder if you text file is changing even if the ip isn't. A simple fix anyways. This will store the ip address and check if that changes, so even if the text file changes nothing will happen if the ip doesn't change.

Code:
;Start timer when mirc starts that checks for changes every 30 seconds
on *:start: .timerdayzprofile 0 30 dayzprofile

;Alias that checks if the file has changed and messages channel. Make sure to update the path for the file and the channel name to message to.
alias dayzprofile {
  set -l %filepath dayzprofile.txt
  set -l %ip $remove($read(%filepath,w,LastMPServer=*),LastMPServer=)
  if (%ip != %dayzprofile) {
    set %dayzprofile %ip
    msg #pball !editcmd !server %ip
  }
}

http://scripting.pball.win
My personal site with some scripts I've released.