Storing custom certification

Is it possible to define a domain that for it, the code won't go to lets encrypt?

I would like to create the certification with another authority for some domains and only store them in my certification DB(Redis).

So I'll need a way to say that do not try to create a certification for them.
Also, would there be an easy way to store them in the Redis and get a notification/log when they are about to expire?

No files, tests, or entry points are named. Start by locating the certificate issuance and Redis storage flows, then clarify the exclusion, custom-certificate retrieval, and expiry-notification requirements; done would mean those behaviors are defined and covered by tests.

Written by the indexing model from the issue text.