About Minhag Hamakom, this has fallen victim to, among other things, mobility. Prior to the industrial revolution, most people were born, lived and died all in the small radius of their hometowns. Jews were the unfortunate exception with expulsions and other tzoros that mixed things about. From this, we have sfardim with notably askenazic names, and askenazim with notably sfardi names. There were “newly settled islands” that saw mihag switch as inflows became rov minyan. (Amsterdam, Istanbul, and the Glenn Avenue shul in Baltimore, among others.
In EY there is an unsettled dispute as to who rules the roost. There were sfardi communites in EY prior to the arrival of Talmidei HaGRA, and so the Sfardi poskim hold a ger or BT in EY is bound to follow the BY. Counter to this is the fact that late in the Geonic period, the residents of EY were deprived of their one day Rosh Hashana by the Chachmei Provence of early Ashkenaz. At present, chaos reins, and there are batei knesset ( generally dati leumi) where “any nusach goes” depending on the flavor of shatz.