From what I can understand, you want to create a rule when you build the OS and have it reside in the rootfs. If that's correct, then you need to add a recipe for it. Store your rule in a directory such as the following "distro/meta-myproject/recipes-core/rfs-myproject/rfs-myproject/myrule.rule". Then, up a level in the rfs-myproject folder you need a rfs-myproject_1.0.0.bb. The file should look like the following
SUMMARY = "MyProject Additional files"
LICENSE = "CLOSED"
PR = "r1"
SRC_URI = "file://my-rule1.rules file://my-rule2.rules \
file://startup.sh file://rc.local "
do_install[nostamp] = "1"
do_unpack[nostamp] = "1"
do_install () {
echo "my-project install task invoked"
install -m 0755 ${WORKDIR}/startup.sh ${D}/home/root/startup.sh
install -m 0777 ${WORKDIR}/rc.local ${D}${sysconfdir}/rc.d/rc.local
install -m 0666 ${WORKDIR}/my-rule1.rules ${D}/etc/udev/rules.d/my-rule1.rules
install -m 0666 ${WORKDIR}/my-rule2.rules ${D}/etc/udev/rules.d/my-rule2.rules
}
FILES_${PN} += " ${sysconfdir}/rc.local"
FILES_${PN} += " /home/root/startup.sh"
FILES_${PN} += " /etc/udev/rules.d/my-rule1.rules"
FILES_${PN} += " /etc/udev/rules.d/my-rule2.rules"
PACKAGES = "${PN}"
PROVIDES = "rfs-my-project"
Hopefully this answers your question, if you need further help please let me know.
Oh yeah, don't forget to include my-project in your local.conf