To add more cities / new cities:

Open the countrylist.xml file

Find the country that you want to add the extra cities to then follow this template, be sure to move the </country> tag after the last city!
You can add as many cities as you like to one country just be sure to add both a name and a city code (and don't forget <city>  </city>!)

CHANGE:
<country countryname="USA" countrycode="US" monetarysymbol="$" monetarycode="USD" monetaryhtmlcode="&#036;" monetarylongname="US Dollar"></country>

TO:
<country countryname="USA" countrycode="US" monetarysymbol="$" monetarycode="USD" monetaryhtmlcode="&#036;" monetarylongname="US Dollar">
			<city name="NEW CITY NAME" code="NEW CITY CODE"></city>
			<city name="NEW CITY NAME2" code="NEW CITY CODE2"></city>
</country>  <<< IMPORTANT If this is not moved to this position then the cities will not work!