How to change position after some reference.

Hi, I'm reading from XML file. And I have a string "RBG" - RedBlueGreen.

Im Instantiating a clone of an prefab depending on that string

 public void ReadAString(string letter,int j, float i, float yPosition)
 {    
         // Get the specific Letter
         switch(letter[j])
         {
         case 'B':
             cube = Item_bbg;
             break;
             
         case 'G':
             cube = Item_gbg;
             break;
             
         case 'O':
             cube = Item_obg;
             break;
             
         case 'P':
             cube = Item_pbg;
             break;
         case 'R':
             cube = Item_rbg;
             break;
         case 'Y':
             cube = Item_ybg;
             break;
             
         default: break;
         }

         //Create a Clone of Item with the specific Prefab and Color
         GameObject clone = Instantiate (cube, new Vector3 (i , yPosition, -1), Quaternion.identity) as GameObject;
         //Add the Clone in a list for a further use
         prefabs.Add(clone);

 }

Now On my second level the string will be GBR or something else like BRG.

How Can I make to not instantiate new objects, but to switch their position according to the new string.

 RBG - This is the string 
 123 - This is the instantiated objects
 
 GRB - This is the string
 312 - new position of instantiated objects