The behavior of the Linux kernel can be changed on the fly using the proc filesystem.
For basic information on changing kernel parameters through the /proc filesystem, read Documentation/sysctl/* in the Linux source.
See some examples of kernel parameter manipulations in /etc/init.d/networking and Странные проблемы доступа на некоторые web-сайты, раздел 3.7.5.
See sysctl.conf(5) for how to set up the boot time kernel configuration through /proc filesystem with /etc/init.d/procps.sh script usually run from /etc/rcS.d/S30procps.sh.