How do you add to an array with "...[]" & reset a selector to avoid duplication

I'm working with Vector3[] but yet apparently .RemoveAt or .Push or .Add won't work. As said in this

Also... since I asked... does this code go through the array and checks whether there are duplicate positions.. then if there is resets the coin position until there is a different position AKA validates until the selector position is unique

 private var    CoinPosSelector        : int; //The randomiser for coin positioning
 private var SpawnPoints            : Vector3[]; //Coordinates for all spawn points
 private var PointsUsed            : Vector3[];
 
 function Start () 
 {
         CoinPosSelector     = Random.Range (1, SpawnPoints.Length);
 
         for (var i : int = 0; i < PointsUsed.Length; i++)
         {
             while(PointsUsed[i] == CoinPosSelector)
             {
             CoinPosSelector     = Random.Range (1, SpawnPoints.Length); //Chooses new position
             }
         }
               PointsUsed.Add(CoinPosSelector); 
 }