public static class PhysicsHandleExtensions

C# refuses an assignment made through a property or indexer that returns a value type. That rules out writing a handle's properties at any such site, however the handle itself was obtained. Each extension here returns the handle from a method instead, which C# does accept as the target of a property assignment. Every handle is a read-only struct carrying nothing but the handle itself. The returned copy therefore addresses the same underlying object, and a property written through it takes effect exactly as if it had been written through a variable.