Does this need clear coat, or does it come pre-finished?

Carbon fiber is porous and will benefit from a clear coat to protect the finish and prevent UV fading over time. If you want maximum durability and gloss retention, apply a quality clear coat after any prep work. The raw carbon will still look good without it, but protective clear adds longevity.

How do I seal the cut edges where the two pieces meet?

Sand the edges smooth before assembly, then seal them with epoxy or the same clear coat you use on the face of the splitter. This prevents moisture from entering the weave at the joint. A clean, sealed edge also looks more finished than raw carbon.

Will the carbon fiber yellow or fade without UV protection?

Real carbon can shift in appearance under direct sunlight without protection. Clear coat with UV inhibitors keeps the finish stable and the weave pattern crisp. If you live in a high-sun climate or plan to park outdoors regularly, protective clear coat is the best investment.