Napoleon’s adjustment of the commandments is an example of his manipulation of language to gain power.
One way that Napoleon uses language to control the animals is through the Seven Commandments. These commandments were initially established as tenets of Animal Farm based on Old Major’s teachings. However, Napoleon is able to change the commandments to allow himself to get more privileges.
An example of this is the 4th commandment, which originally forbade any animal from sleeping in a bed. Beds were supposed to be trappings of humans. Napoleon decided the beds in the farm house seemed quite cozy though, so he changed the rules.
Curiously enough, Clover had not remembered that the Fourth Commandment mentioned sheets; but as it was there on the wall, it must have done so. (ch 6)
The animals do not object because they do not realize anything is wrong. Nothing is written down except the commandments on the wall. If it is on the wall, it must have always been there.
This connection between power and language is one Orwell liked to develop. Since Napoleon is able to control what people see on the barn wall, he is basically able to control the rules and make sure he gets the privileges.