Is this a correct modification?
No. MATCHED_VARS, plural, is correct. MATCHED_VAR is not correct. If you are getting this error it means your version of modsecurity is out of date. You need to upgrade to the latest stable release of modsecurity, which is 2.6.3.
If you are running ASL, ASL will keep modsecurity up to date automatically. If you have disabled automatic updates, just run the command:
Or, if you are not using ASL then will need to upgrade manually. You can do that by running the command:
yum upgrade mod_security
If you have manually setup modsecurity yourself, then you should upgrade via whatever means you used to install it. Its recommended that you upgrade modsecurity regardless, as a number of new attacks can only be protected against using newer features in modsecurity.
asl-lite will try to prevent this from happening, but its not as robust as ASL. ASL was designed to manage modsecurity, asl-lite is just a rule updater so don't rely on it to do software management like ASL will.