That guide is useful, but doesn't seem to mention putting a short piece of heatshrink over the "white" terminal pin, and also over the new yellow wire and the motor tab it is soldered to, in order to ensure that they are fully isolated from each other. When bending the motor terminal tab away from the white pin, you can either bend it inwards or outwards, but if you go outwards (leading the new yellow wire outside the white pin) then you may need to carve a little bit of plastic away from the inside of the gearbox sidewall to make sufficient clearance for the wire. Taking the yellow wire inside the white pin can be easier provided you ensure that the new wire cannot foul the motor shaft or worm. Provided you've insulated everything with heatshrink, you won't have to worry about the physical proximity of the pin and wire.
Jon.