How are the seven commandments being changed ? What are squealer's arguments to justify the changes?

The b7 Commandments are changes a bit at a time for the pig's benefit and by the pigs themselves. Squealer justifies the changes like this;

"Comrades!" [Squealer the pig] cried. "You do not imagine, I hope, that we pigs are doing this in a privilege of selfishness and privilege. Many of us actually dislike milk and apples. I dislike them myself. Our sole object in taking these things is to preserve our health. Milk and apples (this has been proved by Science, comrades) contain substances absolutely necessary to the well-being of a pig. We pigs are brainworkers. The whole managment and organisation of the farm depend on us. Day and night we are watching over your welfare. It is for your sake that we drink that milk and eat those apples. Do you know what would happen if we failed in our duty? Jones would come back! Yes, Jones would come back! Surely, comrades," cried Squealer almost pleadingly, skipping from side to side and whisking his tail, "surely there is no one among you who wants to see Jones come back?"