Non Political – “Are you saying it’s appropriate for a person to act stringently while living in a community where there is an accepted custom to be lenient based on the psak of that community’s Rav?”
– YES! A person can always be machmir above and beyond the community standards, especially if the chumros are based on valid halachs (especially when based on actual psak of Rabbonim). However, it should be done in a private manner, not to make other feel inferior, as mentioned in Shulchan Oruch.
“Are you saying it is assur for the Yom Kippur lady and Seminary girls in your example to do what they did?”
– YES! Not only inappropriate, but probably forbidden once they received a psak from their Rabbonim, to go “psak shopping” would be going against their Rabbonim (which may be even a d’oraysa – Lo sosur min haderech asher yarucha – do not stray from the path that they (the Rabbonim) guide you).