Although I know almost nothing about Cold Fusion, you should be able to test the value of the parameter sent to the page, and do the redirect only if var_file = cripcdir.htm
As for the mod_rewrite solution, I’ll offer this, without testing:
RewriteEngine on
RedirectMatch (.*)/index.cfm?var_file=cripcdir.htm http://www.yourhost.com/cripple.php
The idea is that the first gobbly-gook will match only the exact URL http://www.yourhost.com/index.cfm?var_file=cripcdir.htm
The backslashes are necessary before any special characters.