Access the x, y, z, w components using [0], [1], [2], [3] respectively.
var p : Quaternion; p[3] = 0.5; // the same as p.w = 0.5
using UnityEngine; using System.Collections;
public class ExampleClass : MonoBehaviour { public Quaternion p; void Example() { p[3] = 0.5F; } }