I recently smoked my tail lights and although there is more than one way, I chose the (ostensibly) non permanent way which is to use tint film rather than a spray such as the VHT Nightshades products. Most reputable professional tinters will refuse to do this due to legality issues and it's easier and cheaper to get the film elsewhere and do it yourself.
<Note: I ain't endorsing/recommending or taking any responsibility for what you do to your car. Smoking your lights much like smoking tobacco is a personal choice and I merely endorse freedom and the right to choose).
Anywho. You'll need the following: tint film, scissors, spray bottle (filled with a mix of water and soap), a credit card/squeegee, a microfibre towel, a scapel/stanley knife and a heat gun. Most of which can be seen below.
I also recommend a stool as squatting at your lights for hours at a time is literally a pain in the ass.
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PREPARATION:
Clean your lights. Hose 'em down, soap 'em up, rub 'em with alcohol.
ONE:
Spray the light with your water bottle and peel the protective layer from your tint film before adding it to the light.
TWO:
Scrape over the film using your credit card wrapped in the microfibre towel (to avoid scratching the tint) from the centre of the light out towards the edges to get it to stick a little. Then, trim roughly around the tint film to make it easier to work on further.
THREE:
Start heating the film and smooth it more. Again, work from the centre of the light out towards the edges.
<No picture here. Sorry>.
FOUR:
The film should have stuck a bit by now and conformed to the contours of the light. Get out your scapel/knife and trim around the edges. Don't worry about leaving a little extra around the sides as this will be folded over the edges of the light.
FIVE:
Heat some more. Continue smoothing the film from the centre to the edges. Then, heat the edges and use the card to push the film in over the top, under the bottom and around the sides of the lights.
SIX:
Stand back and take a look and get rid of small air bubbles using a pin. The hardest part to get the film to stick to is the chrome part, so if you have air bubbles on the glass don't worry. They can be removed with a pin or will hopefully disappear from sun and use of the lights.
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Even with tint, your lights should still emit enough light that people know not to run up the back of you.
I have tested this repeatedly by using Subaru's patented anti tail-gate feature (ie. the switch on the steering column) and people still back off.
But when it gets dark and you're parked it's more stealth.
And in daytime, the red is less pronounced.
Anywho, thanks for reading and good luck if you wish to try it. Happy to answer questions or learn how to do it better.
<EDITED ONCE: For grammar reasons>