How do Animal Farm's seven commandments function as a structural device?

In their early euphoria after running Farmer Jones off the farm and taking it over for themselves, the animals, led by the pigs, agree to the Seven Commandments of Animalism. Initially, these commands are: 

1. Whatever goes upon two legs is an enemy.
2. Whatever goes upon four legs, or has wings, is a friend.
3. No animal shall wear clothes.
4. No animal shall sleep in a bed.
5. No animal shall drink alcohol.
6. No animal shall kill any other animal.
7. All animals are equal.

The Commandments function as a structural device because the gradual changes in these commandments mirror the gradual erosion and loss of the ideals of equality and solidarity that united the animals. As Napoleon increasingly betrays the Rebellion and establishes a tyranny, the Commandments are modified to allow him to monopolize power. For example, "no animal shall kill another animal" is amended, allowing Napoleon to kill his opponents. "Whatever goes upon two legs is an enemy" is changed to "four legs good, two legs better." Finally, the animals discover that on the side of the barn where the Commandments were painted only one is left, and it too has been changed. It says "All animals are equal but some are more equal than others." Structurally, this new Commandment signals the complete failure of the Rebellion to maintain any of its ideals. At this point, the pigs are walking on two legs and have become identical to the humans they replaced.