Assign same value to multiple instances of the same prefab

void OnGUI()
{
        GameObject [] pipes = GameObject.FindGameObjectsWithTag("Holder"); //get all holder gameobjects

    foreach(GameObject pipe in pipes) //loop through all holder gameobjects
    {
        SetPipe setPipeScript = pipe.GetComponent<SetPipe>();
            selGridInt = GUI.SelectionGrid(new Rect(50, 70, 100, 500), selGridInt, pipeShape, 1);
        setPipeScript.pipeSelect = selGridInt;
    }
}

public class SetPipe : MonoBehaviour {
    public Transform [] pipe; //put this into an array so it's easier to get stuff from it. just set the size to 7 in the Inspector and fill it with your pipe objects.
    public int pipeSelect;

        void OnMouseOver()
        {
            if (Input.GetMouseButtonDown(0))
            {
            Debug.Log(pipe[pipeSelect].name);
            Instantiate(pipe[pipeSelect], gameObject.transform.position, Quaternion.Euler(0, 0, -90));
                        Destroy(gameObject);
        }
    }
}