You would need a timer that automatically checks the script file for changes (compare $md5 or similar to find out) and then use /reload if it changes.
Ok, I've been looking in the mIRC help file $md5. So, if I do //echo -a $md5(files/fun/fortune.txt) I get 0bca7c6a0c47c954973fd24783c7ce5b.
Can't really figure out how this should say the file has been edited (can't decode it.)
- EDIT -
Didn't saw the Nth part, I now have used //echo -a $md5(files/fun/fortune.txt,2) which appears to be different when I've changed the file.
Hope this'll work! Thanks