When the commandment changes from “no animal shall drink alcohol” to “no animal shall drink alcohol to excess,” it is an example of rewriting history, and significant because drinking alcohol makes the pigs more like humans.
Old Major’s dream includes provisions for avoiding all human behavior. Drinking alcohol is a distinctly human behavior. This commandment change is important for three reasons.
First, it makes the pigs act more human. As they become more and more human-like, they start to be more abusive to the other animals.
Second, alcohol was an indirect cause of the revolution. Jones was a drunkard who did not run his farm efficiently, and when he did not feed the animals they rebelled. So when the pigs begin drinking alcohol and Napoleon thinks he’s dying, it shows that he is becoming more and more like the humans. Notice that only the pigs drink alcohol.
Third, this is another example of propaganda and rewriting history. There was no commandment against alcohol, the animals remember wrong. The commandment is against drinking alcohol to excess.