Well, hold that rosary in your hand and say a couple of prayers while you’re at it, kid. A rosary is not, properly speaking, an article of clothing, and should not be worn as a cool necklace or a colorful fashion accessory. Even “one that makes a statement.”
Personally, I think schools have a right to have a dress code if they wish, and there is no true conflict of conscience here, since “wearing” a rosary is not even recommended, let alone required, by the Catholic faith.
On the angle of “freedom of expression,” OK, go for it; but don’t be surprised if the next thing to come up is the hijab for the Muslim girls, and the kirpan worn by Sikh boys: that’s a “ceremonial daggar.”
We are of one accord...as they say.