When using SSL connection to use external admin store for ADMIN UI with siteminder you can add a certificate but there is no way to remove it or modify it once it has been added.
As it is an SSL setup of the connection between the ADMUI (hosted on an application server) and an external admin store, we are using the default application certificate DB. In our standard installation, using the embedded Jboss server we will use the trustStore.jks certificate DB, located in C:\Program Files\CA\siteminder\adminui\server\default\security by default on Windows.
Currently ADMIN UI do not provide a full certificate management system for SSL external admin store configuration. If you want to remove a certificate, you can use the Java keytool to delete unwanted certificated that you have previously loaded.