Saving data to xml file (I have the loading down)

Hey guys, I've been working on a 'create a class' system similar to Call of Duty. I've managed to make an XML script that will load the classes data from an XML file. This is how the xml is set out:

     <mpdata>
        <class1 name="Assault">
          <data>0</data>
          <data>1</data>
          <data>2</data>
          <data>3</data>
          <data>4</data>
          <data>5</data>
          <data>6</data>
          <data>7</data>
          <data>8</data>
          <data>9</data>
        </class1>
     </mpdata>

Each class is seperated by the 'class1','class2' etc. I wrote this script for loading them on a test basis:

 import System.Xml;
 
 var showData : int;
 
 var class1name : String;
 var class1 : String[];
 
 function Start()
 {
 DataRead();
 }
 
 function DataRead()
 {
     showData = 0;
     class1name = "NULL";
     class1 = null;
 
     var reader:XmlReader = XmlReader.Create("mpdata.xml");
    
       while(reader.Read())
       {
         // CLASS 1
          if(reader.IsStartElement("class1"))
          {
             class1name=reader.GetAttribute("name");
             class1 = new String[10];
 
             for(showData = 0;showData<10;showData++)
             {
                 reader.Read();
                 if(reader.IsStartElement("data"))
                 {
                     class1[showData] = reader.ReadString();
                 }
             }
             showData=0;
          }
          
       }
 }

 function OnGUI()
 {
         GUI.Label(Rect(0,0,200,20), class1name);
         GUI.Label(Rect(0,20,200,100), "Primary Weapon: "+class1[0]);
         GUI.Label(Rect(0,40,200,100), "Primary Sight: "+class1[1]);
         GUI.Label(Rect(0,60,200,100), "Primary Attachment: "+class1[2]);
         GUI.Label(Rect(0,80,200,100), "Secondary Weapon: "+class1[3]);
         GUI.Label(Rect(0,100,200,100), "Secondary Sight: "+class1[4]);
         GUI.Label(Rect(0,120,200,100), "Secondary Attachment: "+class1[5]);
         GUI.Label(Rect(0,140,200,100), "Equipment: "+class1[6]);
         GUI.Label(Rect(0,160,200,100), "Grenade Type: "+class1[7]);
         GUI.Label(Rect(0,180,200,100), "Alpha Ability: "+class1[8]);
         GUI.Label(Rect(0,200,200,100), "Bravo Ability: "+class1[9]);
 }

The information is picked up from another script which loads it into it's own variables, like 'C1PrimaryWeapon' etc, so then I can edit those variables from within the classes menu. My question is how am I able to write to the XML file with the information after it's been changed with the new variables?