I don't see why you wouldn't be able to upgrade the park tickets when you're at the park.
But the room I see no way how you could do an APH rate later. You get an APH rate only when you're booking a room if it's available at that time of booking. You would have to cancel your package, and then re-book a new room at the APH rate on its own. And you should check the terms of your package as any package I've seen always has some form of change or cancellation fees (with the exception of recent times where some could be cancelled/changed without fees due to the pandemic).