Hi.

Considering the famous black marker mod, I just used a black marker to make my LED less bright. Depending on the type of marker, you have to adjust the brightness either by the number of times you paint the LED (if the marker is not covering completely) or the size of the hole you left while painting it (if the marker eliminates 100% of the light where it is applied).
I used a marker of the second type and left a hole of about 0.5 mm in diameter (about 0.02 inch).

cu,
sven