Not eating kitniyos is a minhag, but wearing a hat?! This just got out of hand. So, would a person born into a black hat wearing community need a hatara nedarim if he decides to wear his grandfather’s white or gray hat? Would it be if he wears it once, all the time, for work, or on sheni vehamishi only? I really want to know how people see this.
As to confusion between midrabanan and Torah, isn’t it how we read the story of Adam and Hava making a takono not to _touch_ the grape? You may think that a person who understands the difference will not be confused, but it is easy to imagine someone who did not learn enough to be ignorant about what is meduoraita and what is not.