blanket blocking of URLs with certain GET parameters with one exception

Say I wanted to block all URLs that had, within them, something like
"<script>" in a GET parameter in every directory save one.

To do it in every directory is easy enough - just place an
appropriately written .htaccess file in the root directory. Can I do
that and then place a .htaccess that "undoes", for the directory it's
placed in, what the root .htaccess has done for all the directories?