There are a million tutorials on switchable textures.
Textlights are really simple. Simpy edit your
lights.rad file, which lives in the same place as your ZHLT tools.
GENERIC88A 255 100 100 1000The first column is the texture name, second column contains color and brightness information.
The first 3 subcolumns are the color of the light to be emitted from your texture. I use MS paint to pick a color, and then transcribe the numbers, but you can use just about anything--including a normal light entity in hammer--, to do the same.
Then all that's left is the brightness. I would recommend starting with a low number--50-100--to start, and then work up to the desired brightness.
And that's it. Simple as pie.