There's no reason to be hesitant to disassemble and modify a brass locomotive; and the Sunset locos seem to be well soldered and sturdy. Hopefully these videos will give you the information and confidence that you need to tackle the job yourself. In fact, getting the installation right took me a couple of attempts to find the right combination of miniature connectors and flexible wire to make the installation work - but that is all explained in the film. Be sure to view the videos in order.
There is one omission that I must mention. In hooking up the backup light I forgot to film (or mention) the necessity to include a resistor in the line going to the backup light. This resistor is necessary once the backup light is hooked up directly to the decoder. Use a value of 500 to 1000 ohms and put the resistor in either line of the LED backup light.
In viewing the videos, do not click on the "HD" unless you have high speed internet and a fast computer (dual core processor and good video card); and you still may want to allow the video to buffer before playing.