It's simple to extract etcd data in json(base64) or hex formats with either -w json or --hex flags
ETCDCTL_API=3 etcdctl get /registry/secrets/myns/mykey --print-value-only --hex
ETCDCTL_API=3 etcdctl get /registry/secrets/myns/mykey -w json
But how can one write hex/json extracted data from another etcd instance via cli?
etcdctl put doesn't accept any of these parameters and will store passed value as string