level swap help

I have a game initialize script that instantiates a game object into the scene for level_1 and as I have one of the game objects ion the scene already it gives me two which is what I want. I then copied the level and created a new level called level_2 and would like to have a script to instantiate three more cubes into the scene though if I change the original scrip for level_2 it changes the one for level _1 please could someone help me with this thank you.

function Start ()
{
	Screen.showCursor = false;
}

for (var i : int = 0;i < 1; i++)

{
	Instantiate (gameObject.Find("Asteroid"),Random.insideUnitSphere * 25 + gameObject.Find("Ship").transform.position,Random.rotation);
}

You may do something like this:
var itemCounter: int = 1;

function Start ()
{
Screen.showCursor = false;
}

for (var i : int = 0;i < itemCounter; i++)

{
Instantiate (gameObject.Find(“Asteroid”),Random.insideUnitSphere * 25 + gameObject.Find(“Ship”).transform.position,Random.rotation);
}

In each level, enter a value for itemCounter in the Property Inspector.

thank you ive been on this for hours code is getting to me now
it worked well
thank you

I’ve come to a new problem I have cubes instantiating in my level though I want to do a level change only when the all the asteroids are destroyed though some of the asteroid destroy on their own after a time does anyone have a clue on what I can do and how to do it