Lucky for you - just change the word in one document. If
the footer is identical otherwise, in the remaining 99
documents, just copy and paste the line OR simply open
each document and make the change on the first page that
contains the footer, and all subsequent identical footers
will be changed.
Unfortunately, you do have to open each document
separately - try doing 10 documents at a time - you'll be
done in roughly an hour or less!
Good luck!
Carol