In this picture, four wires may be seen, connecting the PCB to the LEDs support. There are two white and two red LEDs. For one side of the loco, each white LED has its own 620 Ω resistor; they are connected to the PCB by gray wires. The two red LEDs are connected in series with a 560 Ω resistor and connected to the PCB by a yellow wire. The wire common to all the LEDs (anode side) is orange.
Here is this diagram, where we will have to cut tracks, at the dotted lines, to separate the red lights from the white.
But frankly, would it be too expensive for manufacturers to have two straps (as for the rails / panto selection) to make the red lights separable — especially with a 21-pin or PluX interface?