You could set a global variable to the result of the read, then check if it has changed.
Code:
cbs2 {
  var %cbs = $remove($read(c:\CitiNews\news\cbs.txt,nw,*[14]*),[14],[15])
  if %cbs2.last != %cbs {
    set %cbs2.last %cbs
    msg #NewsRoom 47 $mid(%cbs,17)  $left(%cbs,7) ET
  }
}