I have the best way... tail light tint that is a cling... stays on like vinyl, but you can peel it off and reattach at any time! Not sure if there is a premade kit on ebay like we got for the Mustang, but I made mine for the civic and Fiero myself. I got some cling tint from wal-mart, measured and cut... clean the lens with glass cleaner... use a bit of soapy water so the cling can slide. Work it into place and squeegee the water out. Perfect look without the permanent commitment!
I have seen 90% of nightshades tinting jobs look BAD... they never shine like a lens, even with clear. (I have seen a few good ones, but its not easy) Pray you match the coats from side to side, not to mention spitting from the can making dark spots. Sure you can sand and mildly buff, but it will never look as good as a real lens.
Now if you pay to have a shop do it then that is a different story... They can mix black and clear just enough to get it to tint and still lay it down perfectly slick!
The cling however... the hard part is just getting the cut right because the stuff is so darn thick... i still have to retrim mine a bit... darn factory stamped raised letters on the lens... grrrr!
Quick write up on our Mustang...
http://www.cardomain.com/ri...ford-mustang/page-15pics from the fiero install
http://www.cardomain.com/ri...ontiac-fiero/page-12Cling on the tails....

Mustang

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Rescued & resuscitated 1984 Indy Fiero Pace Car #770 presently reversibly modified...LOL!