How relevant can be the major corrections in PhD dissertation? My understanding of major corrections in PhD dissertation is that there can be entire chapters to add to the presented dissertation. However for me it's very hard to understand how much these changes might actually impact the thesis.

Specifically to my situation, I negotiated with my supervisor to limit certain contents that I'm not interested in adding to my dissertation. Apparently he agreed.(1)

However, I'm afraid that these contents can pop up again after the viva, in the form of "major corrections" to the dissertation. In that case, I guess, I will have no chance to negotiate again and I can just accept them or quit the PhD, probably in the worst moment possible. (2) So, can I anticipate this to happen? How can I make sure that "major corrections" will not be used to turn my research to the personal will of the supervisor?

Moreover, since I saw that "minor corrections" could just be revised by the internal committee, I'm afraid that this can happen as well as in the case of "major corrections". But, maybe in this case the corrections cannot be that radical to change the direction of my research. Is this actually possible?

notes

(1) these contents have been forced to me by manipulative moves and have nothing to do with the thesis itself. I added some of them as a compromise to make my supervisor happy enough. I'm rejecting these contents because of the manipulation and because of my personal ethic.

(2) I would not rely too much in the other components of the committee , since they are all under the influence of my supervisor
From this and your other questions, I think you want a fight you can never win. If I remember correctly, you have actually already moved to a different institution and it is just a question of finishing your degree so that you can move on with your career. 

When a king has life and death power over you and makes a demand, the only response is "Yes, your majesty". And you say it with a smile. Even that may not be sufficient, but any other response has a guaranteed outcome. 

I suggest that you write the thesis in such a way that the advisor will accept it. Even, dare I suggest, accept it gladly. Fair it is not. But, you will get to live for another day. 

I don't know exactly how your viva will work or whether you get a chance to respond to any objections made. I hope so. And make the required changes to please the "court". But if not, and the deck is stacked, don't present them with an excuse to condemn you. 

If the situation were otherwise with your advisor being on your side and major revisions suggestions made at the viva (in the public session, not written comments later), I would respond to the reviewers that we (my advisor and myself) considered those and rejected them already for the reasons... 

But that doesn't seem like the situation here. Bowing before a tyrant isn't pleasant. But, perhaps the "madness of the king" will be obvious to others. 

I suspect that, having seen the worst of academic advising, you have some incentive to do a better job of it yourself, provided that you get the chance. Get past this hurdle, however you must. Good luck with it.