Difficulty: Easy. Although a little fiddly.
The cheapest and easiest of the mods thanks to Hobby King.
All you need to decide is what color light you want. Blue, White or Green. I chose green for the retro look.
Hobbyking has excellent instructions in the product images. Follow these.
I had a small issue that came up after I had fitted my LCD screen when I turn the 9X off the lcd would flicker and the unit whistle. It is like the LCD and piezo were getting a small amount of voltage. For now I just put the power switch in the middle position to stop the noise. In a later mod I would like to re-wire the LCD so that it can be faded and turned off and on via software. I'll probably find the issue then, I have a feeling its in the plug somewhere. I cannot find anything similar on the forums so I'm guessing its a dodgy solder or something.
Update: Krzysztof emailed me and pointed out that the main board still gets power when the main switch is off. I am yet to do this myself but he solved the problem by cutting the track here: