Hi,
Extensibility is definitely one of KeyCloak killer features, including
the ability to extend and modify admin console behavior. Unfortunately,
at the moment admin themes couldn't be extended with custom scripts,
contrary to what is stated in the docs.
The issue has been known for months:
https://issues.jboss.org/browse/KEYCLOAK-3052
https://github.com/pedroigor/keycloak-authz/issues/26
I've created a pull request, though the fix is trivial and could be
reimplemented directly.
https://github.com/keycloak/keycloak/pull/2933
Cheers,
Mitya