uGUI

RectTransformのLeft,Right,Top,Bottomをスクリプトから変更する方法.
http://answers.unity.com/answers/1610964/view.html

 using UnityEngine;
 public static class RectTransformExtensions
 {
     public static void SetLeft(this RectTransform rt, float left)
     {
         rt.offsetMin = new Vector2(left, rt.offsetMin.y);
     }

     public static void SetRight(this RectTransform rt, float right)
     {
         rt.offsetMax = new Vector2(-right, rt.offsetMax.y);
     }

     public static void SetTop(this RectTransform rt, float top)
     {
         rt.offsetMax = new Vector2(rt.offsetMax.x, -top);
     }

     public static void SetBottom(this RectTransform rt, float bottom)
     {
         rt.offsetMin = new Vector2(rt.offsetMin.x, bottom);
     }
 }