Is it the same hammer?

Over on this thread on WriteWords, children's author Leila Rasheed asked us all

do people go back to their draft and change the plot of specific scenes while keeping the function of the scene. I think the difference between the function and the plot of a scene is an important one.... it reminds me of the story about the hammer: a man has a hammer; it's the same hammer that belonged to his great-great-great grandfather. In those years, the head of the hammer has been changed many times, and...