what they had was a red lense with a standard 1156 bulb behind it. a separate switch that ran the red light steady or flashing. you could work them over and get everything working good drive the rig around the block and not have them working any more. nobody liked them. or used the red feather. the spot worked like another spot light.
For many here a double headed spot would be clear one side ,red on other side Question could a red light be added to the back side, is that possible or pipe dreaming,,,
I don't believe you could change out the mirror for the red light on this one, although the overall housing looks closer to the clear/red spot housing than most spots with mirrors I have seen. It may be possible to turn it in to one if you happened to have the side with the red light, but I don't know for sure.
I vote with Todd have had many and no mirror change ever found just red light.