Migrating Single Node Rancher to HA (CA certs issue)

Hi.
When my team wanted to install Rancher in our air-gapped environment, we faced issues with the custom certificates that were created for the dedicated machines, so we ended up with a single-node instance running a self-signed certificate.
Recently, we made some progress with the IT department and they’re setting up an internal ACME server that we can use to install Rancher HA.
I read the migration guide in https://rancher.com/blog/2019/2019-01-10-migrating-single-node-2-1-x-to-high-availability/ and saw that the certificates should remain the same during the migration process, so we should use our existing, self signed certificate.

What can we do to replace this self-signed certificate with cert-manager that’ll use our ACME server?
Is it possible to migrate to an HA installation while changing the CA certificate?

Thanks in advance!