If you have CustomBuild 2.0, you can update your exim.conf more easily with:
./build set eximconf yes
./build set eximconf_release 4.2
./build set spamassassin yes
To make use of the newest exim settings and enhancements, you can update your exim.conf by running the following as root:
Note that you only need to run the patch appropriate to the build system you have. If you have custombuild, run the 2nd one. If you don't know what you have, then run them both, as it won't hurt anything if you patch twice.
Note that there are entries in the /etc/exim.conf that should be manually set for your system.
See the readme file for more information. (See the section labelled MANDATORY CHANGES to the SpamBlocker.exim.conf file)