oh I saw this
[h=2]Adding nodes to the Cluster[/h] Login via ssh to the other Proxmox VE nodes. Please note, the node cannot hold any any VM´s. (If yes you will get conflicts with identical VMID´s - to workaround, use vzdump to backup and to restore to a different VMID after the cluster configuration).
I don't want to have downtime isn't there another method except the vzdump one to change VMID?