How to add variables to Components (Nav Mesh Agent)?

Is it possible to add variables to the nav mesh data component. I want my enemy ai to stop at a certain distance from the player but it seems it ignores the rest of my script when I activate the nav mesh agent in my script. Here's the script (note i have commented out the 'myagent' stuff out as I thought it would work but it didn't. I also commented out the movedirection stuff in the function chase so the nav mesh component would work[sorta]):

 var Distance;
 var Target : Transform;
 var lookAtDistance = 25.0;
 var chaseRange = 15.0;
 var attackRange = 1.5;
 var moveSpeed = 5.0;
 var Damping = 6.0;
 var attackRepeatTime = 1;
 
 var TheDamage = 40;
 
 private var attackTime : float;
 //private var myagent;
 
 var controller : CharacterController;
 var gravity : float = 20.0;
 private var MoveDirection : Vector3 = Vector3.zero;
 
 function Start ()
 {
     attackTime = Time.time;
 }
 
 function Update ()
 {
     Distance = Vector3.Distance(Target.position, transform.position);
     
     if (Distance < lookAtDistance)
     {
         lookAt();
     }
     
     if (Distance > lookAtDistance)
     {
         animation.CrossFade("idle");
     }
     
     if (Distance < attackRange)
     {
         attack();
     }
     else if (Distance < chaseRange)
     {
         chase ();
     }
 }
 
 function lookAt ()
 {
     animation.CrossFade("idle");
     //myagent.enabled = !myagent.enabled;
     var rotation = Quaternion.LookRotation(Target.position - transform.position);
     transform.rotation = Quaternion.Slerp(transform.rotation, rotation, Time.deltaTime * Damping);
 }
 
 function chase ()
 {
     animation.CrossFade("run");
     //moveDirection = transform.forward;
     //moveDirection *= moveSpeed;
     //myagent = GetComponent(NavMeshAgent).destination = Target.position;
     GetComponent(NavMeshAgent).destination = Target.position;
     //moveDirection.y -= gravity * Time.deltaTime;
     //controller.Move(moveDirection * Time.deltaTime);
 }
 
 function attack ()
 {
     if (Time.time > attackTime)
     {
         //myagent.enabled = !myagent.enabled;
         animation.CrossFade("attack01");
         Target.SendMessage("ApplyDamage", TheDamage);
         Debug.Log("The Enemy Has Attacked");
         attackTime = Time.time + attackRepeatTime;
     }
 }
 
 function ApplyDamage ()
 {
     chaseRange += 30;
     moveSpeed += 2;
     lookAtDistance += 40;
 }