Hey! Welcome to the forum! This mod is 110% possible, because I have done it before, but It will be harder if you want a different color for each button. In the diagram below
Each of these spots will be the ground, or negative for each different button. You will then need to use the appropriate amount of voltage for each led, I usually pick a 3.6v spot, and you will need to calculate the right amount of resistance you will need. Since you have a Darth Vader 2000, I wouldn't even switch the buttons, the white buttons are see through all ready, and when you apply light to them, they illuminate very nicely, and evenly. Then there are many ways of positioning the leds, you could drill a small hole in each one and put the led in, you could have 4 leds in the center of all the buttons, one led facing each button, It just all depends how you go about it. Let me know if you have any questions!