insert script question

Yes it's possible. To add components to GameObjects you use the AddComponent function. To check distance you can use Distance.

Check the distance and adding the component altogether:

 if (Vector3.Distance(transform.position, target.position) >= 2.0)
     target.AddComponent(MyScript);

You can also use sqrMagnitude instead of Distance which is a bit quicker but less precise,

JS

 var squaredLength : float = Vector3(target.position - transform.position).sqrMagnitude;

CSharp

 float squaredLength = Vector3(target.position - transform.position).sqrMagnitude;

When that is executed you most likely want to add a trigger which says that the object has the component. Here you could use GetComponent, but using something that gets cached is better. So for instance, you can cache the script and tell things to it once it's attached. Extending the previous example a bit:

JS

 private var targetScript : MyScript;

 function Update () {
     if (targetScript==null) {
         if (Vector3.Distance(transform.position, target.position) >= 2.0) {
             // Attach the target script as it wasn't yet attached
             targetScript = target.AddComponent(MyScript);
         }
     } else {
         // The target script is attached and ready for action
         targetScript.someVariable = variableFromThisScript;
     }
 }

CSharp

 using UnityEngine;
 using System.Collections;

 private MyScript targetScript;

 void Update () {
     if (targetScript==null) {
         if (Vector3.Distance(transform.position, target.position) >= 2.0) {
             // Attach the target script as it wasn't yet attached
             targetScript = target.AddComponent(MyScript);
         }
     } else {
         // The target script is attached and ready for action
         targetScript.someVariable = variableFromThisScript;
     }
 }