Vector3 Extensions

public static Vector3 xyz (this Vector3 v, float x, float y, float z) {
    v.x = x;    v.y = y;   v.z = z;
    return v;
}
public static Vector3 xy (this Vector3 v, float x, float y) {
    v.x = x;   v.y = y;
    return v;
}
public static Vector3 xz (this Vector3 v, float x, float z) {
    v.x = x;   v.z = z;
    return v;
}

//calling it
Vector3 v = Vector3.zero;
v.xz(5f,10f);


//============================

public static Vector3 ChangeX (this Transform transform, float x) {
    Vector3 position = transform.position;
    position.x = x;
    transform.position = position;
    return position;
}
// Do the same for ChangeY and ChangeZ
// ...

// Old version
Vector3 position = transform.position;
position.x = 10;
transform.position = position;

// New version
transform.ChangeX(10);

Unity3D - Vector3 to Quaternion

static	vector3	quaternion
vector3.zero	(0, 0, 0)	(0.0, 0.0, 0.0, 1.0)
vector3.back	(0, 0, -1)	(0.0, 0.0, -0.5, 0.9)
vector3.down	(0, -1, 0)	(0.0, -0.5, 0.0, 0.9)
vector3.forward	(0, 0, 1)	(0.0, 0.0, 0.5, 0.9)
vector3.left	(-1, 0, 0)	(-0.5, 0.0, 0.0, 0.9)
vector3.one	(1, 1, 1)	(0.6, 0.2, 0.2, 0.8)
vector3.right	(1, 0, 0)	(0.5, 0.0, 0.0, 0.9)
vector3.up	(0, 1, 0)	(0.0, 0.5, 0.0, 0.9)