On my machine, I use gummiboot for managing the boot process. So, my kernel_post_install() is...
kernel_post_install() {
default_kernel_post_install "$@"
sed -e "s#^linux /vmlinuz-.*#linux /vmlinuz-${target_version//v}#" -i /boot/loader/entries/exherbo.conf
}
Which changes the kernel line in the gummiboot configuration to use the new kernel version, so I don't have to do it by hand.