Can ceramic coatings be applied to trim?
Quick answer: Yes, but the product has to be matched to the material. A paint ceramic is not the right choice for all plastics and rubbers. The right trim coating keeps black plastics darker for longer and makes them easier to clean.
You can coat many types of exterior trim, but the product has to be designed for plastics and rubbers rather than a paint coating pressed into service on everything. The right trim coating helps keep black plastics darker for longer, slows fading, and makes trims easier to clean. The rule is simple: match the coating to the material, and accept that it protects what is there rather than magically reviving badly weathered trim.
Cars carry quite a mix of materials that all get lumped together as trim: textured plastic trims on bumpers, arches, mirror bases and roof rails; gloss black "piano" trims around windows, pillars and spoilers; rubber and plastic window seals and weather strips; plastic grilles and inserts at the front and rear of the car; and occasional bare or brushed metal trims that sit alongside plastics. Different trims live different lives, so the way you protect a rough arch liner is not the same as how you treat a glossy pillar.
Not all ceramics behave well on plastics and rubbers, so it is worth using the right type. A paint-grade ceramic over an unstable trim dressing tends to flake or peel; a dedicated trim coating bonds appropriately and stays consistent for months to a year-plus on textured surfaces. Some installers will skip trim coating entirely on cars where the trim is already badly faded -- the coating cannot bring back depth that has already gone. In those cases, a trim restorer is the right product first; the coating then protects what the restorer has revived.
For the broader "why have ceramic paint protection" answer, see What are the benefits of a ceramic coating?.