Be careful about changing; you probably wouldn't be able to ask him for a reference in the future (or at least, I wouldn't want to!), and with all you've done for him previously (I read your post before you edited it), that would be a loss for you. If you're being taught by him this year aside from the dissertation, it could make your classes for the rest of the year rather awkward.
Try and get down to what it is that seems to have ticked him off - you mentioned a disagreement on how to go about your diss? Try and and discuss how you'd like to approach it, giving your reasons, and be prepared to listen to what he has to say & take it on board. Probably you could come to some mutual agreement.
Do you have someone like a personal tutor or similar you could talk to? They might be able to offer some advice on this, being academics themselves, or even just some other lecturer that you like and feel you could approach for advice.
I also had a bit of a disagreement with my supervisor while doing my BA thesis, but after presenting him with evidence of why I was arguing something the way I was, he backed down & agreed. But you have to be respectful of their experience and expertise.