How do I rotate a player character's gravity 90 degrees on button press? An example of what I want it to do is when you press page down, the gravity of ONE object / character only rotates 90 degrees clockwise. I have tried almost every possible way to get it to work. Please help ASAP. Below is what I currently have as a script that is attached to the character:

var forceToAdd : Vector3 = Vector3(5,5,0);
var obj:GameObject;
private var other:RotateObject;
var rotating : boolean = false;
var changegravityminus :boolean = false;
var changegravityplus :boolean = false;

function Start() {
    other = obj.GetComponent(RotateObject);
}

function Update () {
    if (other.gravity == 1){
       transform.Rotate (0,0,0);
       rigidbody.AddForce (0, 0, 0);
       Physics.gravity = new
       Vector3(0f,-9.81f,0f);
    }

    if (other.gravity == 2){
       transform.Rotate (0,0,90);
       rigidbody.AddForce (0, 0, 0);
       Physics.gravity = new
       Vector3(-9.81f,0f,0f);
    }

    if (other.gravity == 3){
       transform.Rotate (0,0,90);
       rigidbody.AddForce (0, 0, 0);
       Physics.gravity = new
       Vector3(0f,9.81f,0f);
    }

    if (other.gravity == 4){
       transform.Rotate (0,0,90);
       rigidbody.AddForce (0, 0, 0);
       Physics.gravity = new
       Vector3(9.81f,0f,0f);
    }


    if(Input.GetKeyDown (KeyCode.PageUp)&& rotating==false){
       changegravityminus=false;
       rotating=true;
       transform.Rotate (0,0,-90);
       rigidbody.velocity = forceToAdd;
       Physics.gravity =Quaternion.Euler(0, 0, -90) * Physics.gravity;
       rotating=false;
       changegravityminus=true;
    }

    if(Input.GetKeyDown (KeyCode.PageDown)&& rotating==false) {
    rotating=true;
    transform.Rotate (0,0,90);
    rigidbody.velocity = forceToAdd;
    Physics.gravity =Quaternion.Euler(0, 0, 90) * Physics.gravity;
    rotating=false;
    }
}