Problem: have a set of ODT files (tech transfer contracts) that I need to update, but not just now, because they contain a stale proprietary notice that needs to be changed. Perhaps I will never update them all, but only a few. So I prefer to put a notice in each of them to say "hey, you haven't updated notice X yet". They are hundreds in tens of folders and subfolders.
Solution: Luckily they are ODF files, ODF is a zipped XML, a PERL module exists to do incredible tricks.