Yes, Y replacing X reading is correct. It's hard to parse because the Japanese system is itself a mess. The (former) official romanization rules say the name o

Yes, Y replacing X reading is correct. It's hard to parse because the Japanese system is itself a mess. The (former) official romanization rules say the name of this prefecture should be written Aiti but the official practice is to write it as Aichi because that's easier to teach to non-Japanese. Consider that the romanization rules were (iirc) mostly originating from the ministry of education, but that ministries responsible for trade and tourism would naturally prefer to use whatever is easiest for foreign partners to deal with, and could lobby for exceptions since they're revenue centers rather than cost centers. Japan has both a professional bureaucracy under a parliamentary system and de facto one party rule, so (imho) there's much greater potential for policy balkanization of this sort.