How to add Advice to SdkTracerProvider of JavaAgent?

[FWinkler79]

I would like to modify the behavior of the io.opentelemetry.sdk.trace.SdkTracerProvider class that is instantiated by the auto-configuration within the JavaAgent. The reason is that I would like to introduce a second SdkTracer that runs with a different sampling strategy than the original SdkTracer that the original SdkTracerProvider returns.

I have written an extension that tries to add an Advice to the io.opentelemetry.sdk.trace.SdkTracerProvider's get(String instrumentation) method. But it seems the SdkTracerProvider is never called.
I verified that my Advice code is correct by explicitly creating an instance of the SdkTracerProvider in my app and calling its get(...) method. But for some reason, my Advice is not called when the SdkTracerProvider is used by the JavaAgent.

I read about the JavaAgent shading certain classes, i.e. changing their package names, etc. to not clash with the same classes introduced / referenced by the application.

How would I refer to the SdkTracerProvider that the JavaAgent uses under the hood and when it auto-configures the SDK that is then also made available via GlobalOpenTelemetry.get()?

Is it even possible to modify the OpenTelemetry SDK implementations?