Make emissive masks for the buttons that you want to flicker. The masks should be grayscale (or split into RGB components) so that changing their color later would be easy. Multiply each mask by the color you want for the button. Then take the Time input node, pass it to a sine node, clamp it between 0 and 1 and multiply the intensity by the result. Then multiply it by the color result of each mask.
This will give you a slow fade in / fade out
This will give you a hard flickering.
Edit: If you want to control the frequency of the flickering add this parameter:
