Friendly NPC to Enemy (C#)

Okey so I need My NPC that is friendly and you can make conversation with it, to after the last conversation outcome become enemy to PC and start shooting. I need this in C# Would appreciate all the help. Here is my NPC Talk conversation Which work well. And I need to after clicking the second option and second outcome to become unfriendly to PC and starts shooting at him. I got a prefab made also with NPC_Chaser maybe it could be done somehow to replace one NPC with another I don't know, please help. Thank you.

using UnityEngine; using System.Collections;

public class DD_NPC_talk : MonoBehaviour {

 //-------------------------------------------------------------------------
 // ----- Declare Variables 
     
 // Game Objects
 private GameObject go_PC;
 
 //Dialogue Variables
 public string st_NPC_name = "Tower Guard";
 public string st_NPC_inital_text = "You there, Halt where do you think you are going?";
 public string st_PC_response_1 = "Sorry Sir, I was looking for the guards base,\nI want to report a crime";
 public string st_PC_response_2 = "Shove off you trout faced old Fart!!";
 public string st_NPC_outcome1 = "You poor young scamp, it is in the north west part of town, but watch out for the Pirates";
 public string st_NPC_outcome2 = "Well I have never been so insulted, I hope the guards fill you with holes, and the try and fill them with their pork swords!";
 public string st_NPC_return_text = "Leave me alone before I call the guards!";
 
 private string st_NPC_outcome;
 private bool bl_dialogue_on;
 private bool bl_PC_responded;
 private bool bl_conversation_complete;
 
 
 private DD_Level_Manager LM_Script;
 
 //-------------------------------------------------------------------------
 // Start - only called once 
 void Start()
 {
     
     // Find the level manager script
     LM_Script = GameObject.Find("Level_Manager").GetComponent<DD_Level_Manager>();
     
     // Find the PC GameObject
     go_PC = GameObject.Find("PC");        
 }
 
 //-------------------------------------------------------------------------
 // Update is called once per frame
 void Update () 
 {
     // Is the PC in the Scene
     if(go_PC)
     {
         //  when the PC is close Turn the GUI box and start Converstation
         if (Vector3.Distance( transform.position , go_PC.transform.position) < 3 )
         {    
             bl_dialogue_on = true;                        
         }
         else
         {
             bl_dialogue_on = false;    
         }
     }
     else
     {
         go_PC = GameObject.Find("PC");    
     }
     
 
 }//---
 
 // ----- Interface Control GUI Display -----------------------------------------
 void OnGUI()
 {
     if (bl_dialogue_on)
     {        
         // Draw Outline Box
         GUI.Box(new Rect ((Screen.width/2)-200, (Screen.height/2)-150, 400, 250), st_NPC_name);
         
         if (!bl_conversation_complete)
         {                
             if (!bl_PC_responded)
             {                    
                 // NPC Inital text
                 GUI.Label(new Rect ( (Screen.width/2)-160, (Screen.height/2)-120, 350, 50), st_NPC_inital_text);
                 
                 Screen.lockCursor = false;
                                   
                 // PC option 1
                 if ( GUI.Button(new Rect ( (Screen.width/2)-180, (Screen.height/2)-60, 350, 60), st_PC_response_1)  )    
                 {
                        // Set NPC response 1 and flag we have spoken    
                     st_NPC_outcome = st_NPC_outcome1;
                     bl_PC_responded = true;    
                     
                  }
                 
                 // PC option 2                
                 if ( GUI.Button(new  Rect ( (Screen.width/2)-180, (Screen.height/2)+10, 350, 60), st_PC_response_2)  )    
                 {
                     // Set NPC response 1 and flag we have spoken    
                     st_NPC_outcome = st_NPC_outcome2;
                     bl_PC_responded = true;              
                 }    
                }
             else 
             {
                 // bl_PC_responded is now true
                 
                 // Display the NPC response to the PC's Choice
                 GUI.Label(new Rect ( (Screen.width/2)-180, (Screen.height/2)-130, 350, 50), st_NPC_outcome);
                         
                 // PC Goodbye - and set end flag
                 if ( GUI.Button(new Rect ( (Screen.width/2)-180, (Screen.height/2)-60, 350, 60), " Thanks, Goodbye")  )    
                 {        
                      bl_conversation_complete = true    ;
                     Screen.lockCursor = true;
                 }
             }    
         }
         else
         {
             // bl_conversation_complete is now true
             
             // Display text indicating we have spoken
             GUI.Label(new Rect ( (Screen.width/2)-180, (Screen.height/2)-60, 350, 50), st_NPC_return_text);    
         }
     }    
     
 }// ---

}// -----