9I’m going to be working on this much-delayed feature next week, but I agree with the suggestion to use another ACME client for now. Right now the only way to do this with Certbot is to create a CSR using the old key and then use --csr (which won’t work with certbot renew, so it’s less convenient).

sudo certbot certonly –csr /etc/letsencrypt/csr/csr-certbot.pem

https://community.letsencrypt.org/t/how-to-recreate-lets-encrypt-certificate-with-public-key-from-the-past/60096