“Saying that minhag trumps halachah is reducing Rabbinic Judaism to be a collection of customs.”
You said that, not me. I said the minhag is to follow a specific opinion and this decision unilaterally decided to uproot that custom and follow the other opinion instead.
You cite a psak of Rav Ovadia Z’l. So, I will ask again, are you equating these 2, to Rav Ovadia?
Did said high school principle ask HIS Rebbe for his opinion or did he feel that he is sufficiently great enough to issue a psak that goes against the established custom?
Lastly, can you point to a site that carries the psak of those who permit the girls to don tefillin? I would like to read it, especially their resosning, for myself.