A company called Fypon offers exactly what you're after - a wide variety of polyurethane and PVC exterior surrounds. The advantage of polyurethane is that you never risk the rot or warp that's almost inevitable with wood.
To answer your question, you shouldn't have to remove your home's clapboard to install the surrounds. These products attach to existing siding, preventing any water intrusion that could occur from dismantling.
We'd love to see before and after photos of your door and windows! Feel free to post them to Money Pit's Facebook page.