I would check with your local DOT INSPECTION STATION on what you can do or not do regarding adding lights on the trailer bumper area...
Anything on the back of the trailer has to be DOT approved including the light lens etc and things might have to removed in order for you to pass a DOT Safety Inspection. Back-up lights of course can only come on when you are backing up. Pretty sure the law wants that to be tied to your 'going into REVERSE' with your truck and not just be a ON-OFF switch somewhere that you turn on. You safety inspection will catch you on this law...
Back in the day we use to be able to put socks over lights etc but I'm pretty sure that is not allowed now... If the light is mounted it has to work and meet DOT requirements otherwise you have to remove it.
For backing up purposes you might want to install the lights on the sides of the trailer instead of the back bumper areas...
My fifth wheel trailer has those 8-inch scare lights mounted on the both rear sides up near the roof and they really light the camping area great when backing in. I turn mine on from a switch near the inside trailer access door.
Roy Ken