Those kits just sell you plain LEDs. It's no different than just guying a 50 or 100 pack of LEDs anywhere else. They just give you less LEDs and call it a "kit" because they're the size you need and you don't have to look yourself first.
It's possible, but I don't have the time at the moment between working on my cars, school, and mcat studying to keep playing around with additional things until things cool down haha.
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I do LED conversions: Focus / Cougar / Contour / Scion TC / Mustang / Fusion / Milan / Escape