Amazon Certificate Manager (ACM) certificate re-import

Can you replace an existing certificate in ACM with the same hostname (or wildcard) certificate with a different expiration date? Would this allow you to renew an existing certificate and not have to go update all endpoints with that cert?

For instance, customer has *.customer.cloud cert expiring in March 2019. If they obtain another *.customer.cloud cert expiring in March 2021, can they use the re-import option in ACM and replace the 2019 cert prior to its expiration with the 2021 cert? Would the 2021 cert then be pushed out to all ELBs where the 2019 cert existed?

My intuition is telling me that the new cert has a new public key, so it will not be able to re-imported over the existing 2019 cert. The customer will have to Import the 2021 cert as a new cert and then manually change their AWS Elastic Loadbalancer (ELBs) to use the new cert. Is that correct?