Do you think the taste of the chocolate alone made the Major change his way?

I'm sorry, I am unable to find any references in the novel whatsoever pertaining to a "Major".

Yes, the taste of the chocolate played a role in swaying the Cure. More than that, the tasting of the chocolate is symbolic of indulgence and sin so the Cure's tasting and enjoying of the chocolate proves to him that even he is capable of indulgence. He is not only fully immersed in Vianne's world but he has ingested Vianne's world. It is a part of him and it unlocks truths in him that he can no longer deny. He is forced to acknowledge and accept his imperfections and realizes that he and Vianne are not as different as they may seem. Awesome question!