Ah, no, that's exactly what I was after for my use-case, thanks Matěj Novotný.

As a quick summary of what I'm doing if you are interested:

• I write integration tests for a CDI based framework
• In my tests I define beans with which I test the functionality
• I must not have all beans in the container, but only the ones I need for the specific test
• Marking them as @Alternative and then using SeContainerInitializer#selectAlternatives does not work, as they would only be enabled in the synthetic bean archive unless I disable archive isolation
• Using @Priority to enable the alternatives globally also doesn't work, as this requires compile-time definition of what should be enabled and I need it at runtime

So my current tactic was (and is, just with the new method you told me about) to have all such beans annotated with @Alternative and then in the custom CDI extension add the types I need to the container.

So now I do

beans.each {
    beforeBeanDiscovery
            .addAnnotatedType(it, null)
            .remove { it.annotationType() == Alternative }
}

as addAnnotatedType(AnnotatedType<?>, String) does not return an AnnotatedTypeConfigurator where I could remove the @Alternative annotation.

This works fine so far (except you see another flaw in this now I missed).