I'm running a private regtest network on GCP. I generated a list of 2000 vanity testnet addresses ordered sequentially from prefixes mooo1 to n2ooo with their respective pub/priv key pairs, and to prevent complications, I want to only have one private key for each node (change in outgoing transactions are sent to the original address). Because there's no security concern in my setting (it's just a performance test, no money or attacker is involved), I want to make each bitcoind instance only use a single private key for all transactions, and not generate new addresses through an HD wallet. This is because viewing transactions is much more streamlined. I can tell which node is sending bitcoins to which other node, and diagnose issues more easily. Is there an option in bitcoind to only use a single private key?