When swapping the joysticks on my drifting JoyCons, I kind of snapped the ribbon connecting the rail buttons to the controller itself. They were both left JoyCons, but the site I sourced the boards from only sold pairs.
The swap worked much like the joystick swap. You don’t have to remove the battery tray, but it helps as the ZIF connector is right under it. You also have to be careful with folding the ribbon back into the JoyCon so you don’t snap it again.
But, in and out, quick 20 minute adventure to swap out rail button boards on two JoyCons.