This repository contains a "CoreOS stream metadata" file which implements openshift/os#477 which is a subset of the larger bootimage enhancement: openshift/enhancements#201
The all purpose CoreOS building and testing tool is coreos-assembler. It contains the plume command.
To update the bootimage for one or more architectures, use e.g.
$ plume cosa2stream --target rhcos-4.8.json --distro rhcos x86_64=48.83.202102230316-0 s390x=47.83.202102090311-0 ppc64le=47.83.202102091015-0
The initial file rhcos-4.8.json was generated this way:
$ plume cosa2stream --name rhcos-4.8 --distro rhcos x86_64=48.83.202102230316-0 s390x=47.83.202102090311-0 ppc64le=47.83.202102091015-0 > rhcos-4.8.json
But the plume --target command is designed to read and write an existing file, so there shouldn't generally be a need to use this invocation again.