How to change character when first character dies ?,Change Character Model mid game ?

Why not just simply have character prefabs and switch between them?

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class NewBehaviourScript : MonoBehaviour
 {
    public bool PlayerDead;//Determine PlayerDead in your health script
     public GameObject InitialPlayer;//Drag the initial player into this slot
    public GameObject PlayerToSwitchTo;
   
     // Update is called once per frame
     void Update()
     {
         if (PlayerDead)
         {
             Instantiate(PlayerToSwitchTo, InitialPlayer.transform.position, Quaternion.identity);
             Destroy(InitialPlayer);
         }
     }
 }