Aha! Managed to find some code already posted here that pretty much did what I need:

function changeMaterial01(){
    var changeMaterial01 : Material = Jeff.renderer.material;
    Jeff.renderer.material = Material01;
}

Hi There! If I understand what you're saying, you want multiple instantiated objects with the same texture? That is quite possible. Here's a quick demo (requires a gameobject and 3 textures).

using UnityEngine;

public class lol : MonoBehaviour
{

public GameObject MyPrefab;
public Texture[] Textures = new Texture[] { null, null, null };
private GameObject[] _prefabs = new GameObject[3];
void Start()
{
    _prefabs[0] = (GameObject)Instantiate(MyPrefab, Vector3.zero, new Quaternion(0, 0, 0, 0));
    _prefabs[1] = (GameObject)Instantiate(MyPrefab, Vector3.left, new Quaternion(0, 0, 0, 0));
    _prefabs[2] = (GameObject)Instantiate(MyPrefab, Vector3.right, new Quaternion(0, 0, 0, 0));

    for (int i = 0; i < _prefabs.Length; i++)
    {
        GameObject prefab = _prefabs[i];
        prefab.GetComponent<MeshRenderer>().material.mainTexture = Textures[i];
    }
}
}

Here's some things to note: Each time you change the texture on a gameobject when unity is running, Unity creates a temporary instantiated material of that object. This means your changes don't go to the hard drive, and you're pretty much making each object completely seperate (think individual draw-calls if you want to use this on a phone or iPad in the future).

You can't directly access an objects material, as it is rendered through either a Mesh Renderer or Skinned Mesh Renderer (for characters). A material isn't a component, so you can't use GetComponent on it directly.