Stocked trout are like snowflakes. Some will go hunkering away as soon as the sinkers start hitting the water, and some will go into a feeding frenzy. And most will be somewhere in between. It's all about where you'll be fishing.
Opening day is the coming out party for ATWs. If it is stocked and close to access, it will be crowded with many anglers of all persuasions. In these areas, if fish are to be had, they will be had on attractor patterns (junk flies) for the most part. You aren't going to see a lot of rises with the banks lined with anglers. If you can find distance from the crowds, the streams will fish mostly the same as any other day.
Though I stubbornly have taken the long rod when joining traditional anglers for Opening Day, I would have been better served by taking an ultralite spin outfit and powerbait, particularly if my goal was to just catch fish.