Finally, someone besides me jokes about the cast changes!
Though remember that in the world of Collinwood/Collinsport the characters are still the same characters regardless of who plays them. It's only in the real world of the studio that they're different. And we've stressed that those two worlds shouldn't really cross over into one another.
We change all sorts of things about people's thoughts, motives, histories, and actions for the sake of the jokes... I make no reference to the actors or cast changes or the real world. I just like the idea of jokingly calling attention to the remarkable change in some of the characters' appearances... and explaining it not in terms of the real world, which shouldn't intrude, but in terms of the fictional one.