Have you recreated a game after you edited directly the scenario, changing the city name (which is born by a structure of type city as you know). Normally, this should work, even if this is the manual way of doing it.
To use CSVSplitter for cities, you should use the Script Cities tab, this will create a file from your csv, that you should rename (examples) Cities1809.inc
If Cities1809.inc is the name of the include file called in the 1809 Setup... Check the include directory, you should find one such .inc for each scenario, just replace the old one with you. Then you have to recreate the scenario. There is doc about that, as this is another story