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,

I 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);	
		}
	}	
	
}// ---

}// -----

Yes you could replace one with the other.

You would use the Instantiate command to create the new one.
You would use the Destroy command to get rid of the old one (DestroyImmediate might be necessary for it to look clean)

Another approach would be to simply have another component that is your attack behavior. You disable the talk component and enable the attack one.