I think that one way the Pigs rewrite history is to ensure that they are always in the position of power. This job falls largely to Squealer, who is able to spin anything so that the Pigs, and in particular Napoleon, is always in the right. The pigs rewrite history by being able to stretch the truth so that the animals, unassuming of the ulterior motives, end up believing that which is said by Squealer and the pigs. An example of this would be when the Pigs move into the house and while it might on face value violate a tenet of Animalism, Squealer argues that it is needed for the Pigs to have space in order to work and do the planning for the farm's benefit. This is an example of rewriting history, or Animalism, in order to benefit the pigs while the other animals fail to either recognize or act on what is being done. In Chapter 7, Squealer rewrites history in constructing Snowball as an agent of Jones, and thereby opening the door to anyone who agreed with him as an enemy of the farm. Snowball was instrumental to the farm's success, but once deemed an adversary by Napoleon, Squealer embraces the task of rewriting the narrative as Snowball being an enemy of the farm and ensuring that anyone who supported him is treated to the ultimate penalty in death. It is in this scene where the Orwell shows how much authority benefits when it is able to rewrite and construct history in a manner that legitimizes its own authority.