This script has been tested on Unity 2019.4.30f1 or later (Probably works on older versions too)

How to use

• Create windows shortcut of UpdateUnityDefaultScript.bat and change it's properties to open with admin rights
• Or directly open UpdateUnityDefaultScript.bat with admin rights

How to customize scripts

1. Go to C:\Program Files\Unity\Editor[Version]\Editor\Data\Resources\ScriptTemplates (This is a Unity default path) and copy the script you want to modify
2. Go to .Scripts/ModifiedScripts/ and paste the script
3. Open the file and modify it

Example

81-C# Script-NewBehaviourScript.cs.txt

• Default:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

    #ROOTNAMESPACEBEGIN#
public class #SCRIPTNAME# : MonoBehaviour
{
    // Start is called before the first frame update
    void Start()
    {
        #NOTRIM#
    }

    // Update is called once per frame
    void Update()
    {
        #NOTRIM#
    }
}
#ROOTNAMESPACEEND#

• Custom:

using UnityEngine;

public class #SCRIPTNAME# : MonoBehaviour {
    private void Start() {}

    private void Update() {}
}

How does it work

The script check the registers to find unity location and copy paste the modified script to that location