How can we change according to time, that is kind of opportunism.
Changing with time is not always being opportunistic, many times it is inevitable and prudent!
Those are not called changes but up-gradations/improvements. Those are natural if some one finds himself lacking/wanting in a particular field. Changing frequently with ones own stand is certainly opportunism.
Your statement is not wrong either, also there cannot be a politically correct answer to such question. What you are talking about is a typical scenario that one usually encounters in working life and in general as a whole.
But what we are talking about is sudden fluctuations and changes around us or in our dealings or whatever....its an exhaustive topic! With every situation, probably the answer would be different.