Consider someone who changed his viewpoints, behavior the way he dressed, the way he behaved etc. all of a sudden. Maybe after a revolution or after having a trip somewhere, he turned out to be a new one. In our language we say the person changed 180 degree! Could you kindly help me with it?
The first term that occurs to me is "fickle", which would cover a lot of the things I think you're referring to. Such a person can also be "changeable", "capricious", "faddish". Somebody who is easily influenced to change their behaviour by new acquaintances and experiences is often said to be "impressionable".
In English you can say that somebody has changed their mind/opinion 180 degrees, meaning they now hold the opposite point of view. However it's not common and doesn't necessarily mean that this is a habit of theirs or a particular character trait.
not a teacher