I think I’ll keep it similar to what I’ve got designed for the shield switching. You’ll define your “Sources”, in your case HD Radio, and Internal Audio. But instead of selecting “Input 1” and “Input 2”, you’ll changed them to be intents. Then when configuring your button for HD Radio, you’ll select the source “HD Radio”. Then when the button is pressed it switches to that source and stays there until you play some internal music or something else that needs the “Internal Source”
That’s what I’ve started with the shield, it shouldn’t be to much to add your custom intent options.