I checked it out - an interesting approach. I've always preferred to put bulbs in headlights, where they belong. I run DC, so I remove the circuit board in the tender, replacing it with a TTR constant lighting unit that puts out 1.5v DC. Using existing wiring, I run the output to the smokebox, and hook a 1.5vmini-bulb to it. And yes, you do have to remove the boiler shell. The Bachmann 2-8-0 uses a rather peculiar arrangement to gather the light from the bulb hidden in the boiler weight. It can usally be carefully removed by grasping the headlight housing with one hand and twisting the light pipe (a cup shape with a rod extending into the headlight through the boiler front). Once removed, the micro bulb can be slipped through the hole in the boiler front and into the back of the headlight housing. This places the bulb in about the right position for a real bulb, into the recess in the headlight lens. Reassemble everything, and replace the boiler shell.
Something similar could be done in DCC with an appropriate resistor attached to one of the bulb leads, and stashed in the smokebox...