You will need tint spray (tint adhesive), a smoother (like a plastic bondo scraper), and a bottle of baby shampoo mixed with water. Clean the tail lights, apply tint spray, apply tint, coat in water/baby shampoo mixture, smooth out with smoother.
One major problem I do see with this idea though is that applying tint to outside surfaces will not be very durable. Plan on redoing the tint at least every other year.
I sent a link to this thread to my husband for further "professional tinter" input and suggested that he could make a pattern and cut these with his vinyl cutter using materials we already keep in stock. I'll let you know what his response is when I receive it. (I am currently out of town without cell service.)