How to modify kubeconfig for system:admin user after adding API certificate in OpenShift 4?

Issue

• kubeconfig file is not missing but it is necessary to modify it after adding the API server certificate.
• After adding the API server certificate by the steps introduced in the document, it is impossible to access the cluster with the original kubeconfig file for the following error:

$ oc login -u system:admin --kubeconfig=<install directory>/auth/kubeconfig
error: username system:admin is invalid for basic auth

• I want to keep using the original kubeconfig file as it has a 10-year expiration, yet the re-created kubeconfig file has only no more than 14-months expiration.