Single switch light system? Is there a headlight/taillight system that can be turned on with one switch, rather than turning on 2-4 lights each individually?
It's an easy modification to make if they use the same voltage and have simple on/off switches. I've done it on an e-bike. But I'd only make the primary tail light share a switch with the headlight. Without a backup you've introduced a single point of failure which is a bad thing even if your wiring is rock solid. A single wire heading to (multiple) rear lights could break and you wouldn't even know you were showing no light from behind. 

You could look into motion sensing lights for the back (they may also exist for low power front lights), especially as your secondary lights so you only have to switch two lights on. Some of the solar rear lights have this feature.