The commandments are changed in Chapter 8 so that they become lenient where they were once absolute. Instead of "No animal shall drink alchohol" and "No animal shall kill another animal", the commandments become "No animal shall drink alchohol to excess" and "No animal shall kill another animal without cause."
These changes essentially allow the pigs to do what they want. In fact, they are changing the commandments after they have already broken them, excusing their breeches by simply changing the law to allow for their "bad behavior".
Soon the pigs go so far as to replace all of the commandments with the single commandment:
"All animals are equal, but some animals are more equal than others."
At this point the democratic institutions and egalitarian nature of the farm have been abandoned and replaced by a self-serving, totalitarian regime.