Revoke and generate distribution certification will existing apps available still?

Hello all professions,

I'm now facing an problem with distribution certification expiration for the enterprise account.

We're using enterprise account for publishing some internal apps for our organization without uploading to AppStore but by other platforms, but both cert and profile have 1 year expiration and now it's about to expire. So we're going to extend the app expiration date now.

Read some articles that the best practice is renewing cert before it expired, for some reasons that we CANNOT add new certifications if we're not revoking any of existing certs, so what we are going to do is:

We will revoke the cert first let's say certA, and then create a new cert with all configurations as same as certA let's say certB and then distribute new app version by certB.

If we're going to do so, then the question comes:

1. Will the existing installed apps distributed by certA still available? (if it has couple months to be expired for certA)

2. Continue with question1, if no, all existing apps will not be available anymore, then what's the best practice for us to manage certs and app for the users without cert renewing downtime?

3. Will there be any issue if we user another cert let's say certC just create now to distribute new app version without revoking current certA? such as it will be recognized a brand new app, etc

thanks all