c3os is a container-based OS, if you want to change c3os and add a package it is required to build only a docker image.
For example:
FROM quay.io/c3os/c3os:opensuse-latest
RUN zypper in -y ...
RUN export VERSION="my-version"
RUN envsubst '${VERSION}' </etc/os-release
The image can be then used with c3os upgrade or with system-upgrade-controller for upgrades within Kubernetes.