If your taillights are too dark, it’s definitely an issue that you need to rectify as soon as possible. According to traffic laws across states, your taillights need to be visible up to 1000 feet away. Now, this might sound excessive, but it’s purely for safety reasons.
Many car-mod enthusiasts love the look of a sleek, incognito vehicle and will choose to cover their taillights to make them darker. However, if you’re doing it yourself, there’s a chance that you can make them too dark, which can not only put you in harm’s way, but also land you a fine from your local traffic cops.
If you’ve used a spray product on your taillight cover, you can try and scrape it off by wet sanding or using a hard grit sand paper. However, depending on how many layers you’ve used, you might have to replace the covers entirely.
Instead of using a spray product, try opt for a tint film, which is also removable.
Most glued lamps can be dissassembled by heating them in the oven @ approx. 250 degrees for about 10 minutes to soften the glue… then pry them open with a screw driver. I’ve done it with Mazda aftermarket lamps. It’s a pain, but it’s a lot cleaner than spraying the outside, FYI. Tint film (externally applied) is a better solution IMHO, especially in a state that does not allow tinted tails – it’s nearly invisible after installation and if you get hassled you can peel it right off.
Lamin-X (re-sold all over) has a great selection of headlight and tail light films in a variety of colors and degrees of darkness.
Personally, I’d strip off ALL of the sprayed-on stuf (if you can) and go with film, esp, in Cali (I hear that state is vigilant on enforcing tail light violations). If Lamin-X does not make a pre-cut kit for your make/model you can get uncut sheets as well.