For all those asking about adding custom cities into the weather tab I suggest you read this thread:
Essentially you can edit the xml file and add any city you want...... however you will only get a weather forecast for it if it is on the HTC list in Accuweather.
If you want to check whether your city will dispaly with the weather then use this site:
Only took me a couple of days of searching to find this out.
change the end code to match your desired location
Location: UK (giffgaff)
Device: SGS4 and P7510