The transaction for submitting the new stake pool registration certificate needs to be signed with 4 signing keys:
the cold key
the payment key (to pay the transaction fees)
the first stake pool owner stake key
the hardware wallet stake key (the new pool owner)
When not using a hardware wallet, the transaction to submit a stake pool registration certificate can be signed with one command. But because of the way the hardware wallet can sign transactions, the transaction must be witnessed by every signing key, and then all the witness files must be combined into a signed transaction file, which will be submitted to the blockchain.
Create and execute the following scripts in a subfolder of transactions (for example pool-update):
The transaction-assemble.sh will create the signed transaction file, which needs to be submitted to the blockchain with the following script (submit-sh):