I think if it were me I would work on uncovering the face area. I wouldn't go too awfully far because it looks like there are some pretty good size active veins in that candling picture.Ok here's how the little guy looks as of right now. Do you think I should widen the hole around his face some more and take a bit more shell off? He is yawning less. he's chirping up a storm. I did get a candling picture.
At this stage I would be concerned that if it was able to turn to try and zip it could block its air supply.
You know best from what you're looking at though.. again it's hard to tell in the picture if the duckling is going to be stuck or not.