https://www.schmiedmann.com/ has some well-made & well-fitting diffusers for the dual exhaust. I've seen rear spoilers/wings with brake lights but not a diffuser - seems the light would be a bit low to be of much good!
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2015 BMW 228i in EstorilBlau II Metallic / Terra Dakota Leather - 6-speed manual, M Sport Package, Cold Weather Package, Lighting Package, Premium Package, Harman Kardon premium sound, Anti-theft alarm system, Blue Metallic Matt Accent Moldings, Aluminum Hexagon Interior Strips, Anthracite Headlining