My flock is 20 months old. They have been living in their coop for 15 months. Every morning I open the (human-sized) door and they come tumbling out to go about their business; free ranging all day. At night, they hop back in the coop to put themselves to bed. My hens have always been faithful about going back in the coop to lay their eggs. Now we need to add a pop door; not only to keep the coop warmer during the winter, but to keep the cows from raiding the coop every chance they get. My concern is that the hens will be confused when they find the big door closed and not know to use the pop door to get in and out to the nestboxes. My flock is very set in their ways. In fact, every morning when I go to the coop to let them out the minute they hear me click the lock I can hear them jumping down from the roosts and lining up to be let out. Most always they come out of the coop in the same order. I feel like it's too late to change anything with this flock, because they don't take well to change. Is there a way to make the transition to the pop door go more smoothly, with the hens using it to go back inside?