[arch-general] Pacman trigger

Is there some app that will do some actions on updating some software ? Like for example, I want that in /usr/lib/firefox-<version>/defaults/preferences/firefox.js user agent is set to Firefox/<version> instead of its brand name ? Or copy the previous version of kernel to /boot/stable before update ? -- Nilesh Govindarajan Site & Server Adminstrator www.itech7.com