How to override the time zone for some particular country? How can I get my Android device to show a different time zone for a particular country?

So, when I pick the country I’d see the overridden time zone instead of the default one.

I have a rooted device with system version 4.4.2

Edit

Say I want to pick London, Dublin with automatic time zone disabled, but rather that showing GMT+0:00, I want my device to show something else, say GTM+0:30, is that possible with a rooted device?

Also I want that "fake" time zone to be reflected in the clock as if it were the actual time zone. So when it's 12:00 in London I want my device to show 12:30 instead.
First of all: There is no official way to change time zones because they are provided from the server so you would need to add the time zones there.

Second: if you go into settings -> date and time you can change the time there and subtract/add the amount of time you wanted the time zone to display.

With something like UCCW and a status bar customizer you could customize widgets. You could, of course, create a clock with an offset and display a text next to it saying: GMT +0:30 but this would not be in the entire android UI.

If you have a status bar customizer like Omega Status Bar you can customize your own status bar and set/remove text so you could set the time in android to be 30  minutes less and display 5 "GMT -0:30" next to the clock on your status bar.

If you have any questions feel free to ask.