I'd like to prepare multiple yaml files customizing arguments of flannel (DaemonSet) and run the flannel pod of the node with yaml matching the condition expressed by the label. Can I label a worker node before joining Kubernetes master ?
You can specify --node-labels when you're kubelet is starting, which will apply the labels to the nodes; but ONLY during registration.
This will not work if your kubelet is starting up and the node is already a member of the cluster.