Unable to modify the Web.Config file settings using customization plug-in

Here is the source code:

using System;
using PX.Data;
using System.Collections.Specialized;
using Customization;
using System.Web.Security;
using System.IO;
using PX.Common;
using PX.Web.Customization;


namespace ChangeWebConfig
{

    //Customization plugin is used to execute custom actions after customization project was published  
    public class MyPlugIn : CustomizationPlugin
    {
        //This method executed right after website files were updated, but before website was restarted
        //Method invoked on each cluster node in cluster environment
        //Method invoked only if runtimecompilation is enabled
        //Do not access custom code published to bin folder, it may not be loaded yet
        public override void OnPublished()
        {
            this.WriteLog("OnPublished Event");

            String file = File.ReadAllText(Path.Combine(PX.Data.Update.PXInstanceHelper.RootFolder, "packages.config"));
            file = webconfig.Replace("<activeDirectory enabled=\"false\" path = \"\" user = \"\"  password = \"\" />","<activeDirectory enabled=\"false\" path = \"TESTPath\" user = \"TestUser\"  password = \"TestPasswod\" />");



            File.WriteAllText(Path.Combine(PX.Data.Update.PXInstanceHelper.RootFolder, "packages.config"), file);
        }

        //This method executed after customization was published and website was restarted.  
        public override void UpdateDatabase()
        {
            this.WriteLog("UpdateDatabase Event");
        }
    }
}

Hi @Dmitrii Naumov  Thanks for the reply.

But, how can we achieve this, if not with the customization?

@Dmitrii Naumov 

We integrating ERP with Azure Active Directory and it seems we need to necessary modifications in the Web.config file, and then we found the above article to achieve, but when we try it is not working.