RE: Headliner Removal
I had my headliner replaced a while back, because it was separating from the sun roof trim. I was there at the dealer when they replaced it, and I helped the guys get it back in the truck. You'll have to start by removing all the pillars, like the "A" Pillar where the handle is when you get in the truck, and also the "B" Pillar where your seat belt is bolted to. I don't think you'll have to remove anything from the rear of the cab, if your just lowering it low enough to get the lights installed. It shouldn't just fall down either, because there is velcro holding it up, so you may have to give it a slight tug/pull to get it to drop. Just be careful that you don't damage any of the ceiling light connectors. Hope this helps.