A yid who is visiting eretz yisroel for yom tov still keeps two days of yom tov due to the minhag hamakom of where he lives.
In private. In public someone from Eretz Yisroel visiting chutz la’aretz cannot violate the second day of Yom Tov.
A woman from Meah Shearim visiting Brooklyn continues to wear her shawl even though it is not the minhag there.
There’s no minhag against wearing a shawl in Brooklyn.