Changing GUITexture's position through code (relative to screen)

Found it. pixelInset must always be reset as a new Rect variable in order for the changes to apply. Here's the end result:

 using UnityEngine;
 using System.Collections;
 
 public class GUITextureScript : MonoBehaviour
 {
     public GUITexture texture;
     bool menuOut;
     
     // Use this for initialization
     void Start ()
     {
         menuOut = false;
         texture.guiTexture.pixelInset = new Rect(600, 0, 1, 1);
     }
     
     // Update is called once per frame
     void Update ()
     {
         if (Input.GetKeyDown ("m"))
         {
             showMenu ();
         }
     }
     
     void showMenu()
     {
         float texPosY = texture.guiTexture.pixelInset.y;
         float texWidth = texture.guiTexture.pixelInset.width;
         float texHeight = texture.guiTexture.pixelInset.height;
         if (!menuOut)
         {
             texture.guiTexture.pixelInset = new Rect(400.0f, texPosY, texWidth, texHeight);
             menuOut = true;
         }
         else
         {
             texture.guiTexture.pixelInset = new Rect(600.0f, texPosY, texWidth, texHeight);
             menuOut = false;
         }
     }
 }