If I understand correctly, you want to back up the full state of a node except its wallet, and restore it with a new wallet? If so the answer is that you can so this by stopping the node and making a backup of all the files in the blockchain directory except the wallet.dat file that contains the private keys and the wallet directory.
When you restore from this backup a new wallet file will need to be created, and you should run multichaind with the options -walletdbversion=2 -rescan to initiate this correctly with a new address. The new address will need to be granted connect permissions to join the network, and after that everything should work fine.
