You should be able to change the Auth0 app using the following command:

echo '{"issuer": "https://dev-06bzs1cu.us.auth0.com/", "clientId": "BgFUlOC2NZhEXunM5feV9YkG2KJv2bTL", 
  "clientSecret": "sndlETfH0V8YJfawZJfB_z1Y4rj3T10rq5YVuNLgtb9WVgfp60pQA-ibjS0r7NGG"}' | http POST :8080/api/configure

The client ID and client secret in the above command are different from the defaults. Ideally, they'd be used after you run this command and going to http://localhost:8080 does not redirect you to the "Bootiful Login" app. Instead, it redirects you to an app called "Spring Boot".

I asked Rob Winch why this doesn't work. His response:

That isn't going to work since the code is trying to modify the registry after all the beans are wired. It will not reinject all the Beans again unless context is refreshed at which point the bean definitions from the Configuration will be re-loaded.

Do you only ever need a single ClientRegistration (no concerns around concurrency?)? If so, I recommend creating a MutableDelegatingClientRegistrationRepository. First it delegates all its work to another ClientRegistrationRepository. Second it allows you to set the delegate. That means you can get a reference to MutableDelegatingClientRegistrationRepository and set the ClientRegistrationRepository on MutableDelegatingClientRegistrationRepository.

If you are worried about concurrency you'd likely need to re-implement InMemoryClientRegistrationRepository since it isn't made for extension. The new implementation would have save/deleteRegistration methods. This would allow you to add/remove entries into the Registration. You'd need to refer to it by the class since save/delete methods are not on the interface. Alternatively you'd need to create your own interface that extends the ClientRegistrationRepository. Note security does not need to add/remove entries which is why it isn't on our interface (we try and keep the interfaces as to what Security needs to get the job done).