Change headers for original request in a authorization template out of process adapter?

So I have an out of process mixer adapter that handles authorization using an external service. The adapter works fine based on the out of process adapter walk-through but I need to set an additional header to the original request based on the response from external service.

Currently there is no HandleAuthorizationResponse in the proto https://github.com/istio/istio/blob/7c05efeab5f3ff583b42ac512de3dcf1b6618fc1/mixer/template/authorization/template_handler_service.proto#L75

Is there any way to do this? I did come across this Route directive adapter guide that uses a custom template and uses responseHeaderOperations. https://github.com/istio/istio/wiki/Route-directive-adapter-development-guide
Is it possible to replicate this using existing authorization template?