Modify Web.Config using visual studio or powershell to specific web application

I have a problem in modifying web.config to specific web application I've search and try so many solution, when i deploy, the modification still affect to all existing web application

here is my code part of my code :

public override void FeatureActivated(SPFeatureReceiverProperties properties)
        {            
            SPWebService service = SPWebService.ContentService;
            SPWebConfigModification myModification = new SPWebConfigModification();            
            
            SPSite site = new SPSite("http://win-a52s8epvot4:888/");
            SPWeb web = site.OpenWeb();

            myModification.Path = "configuration/appSettings";
            myModification.Name = "add[@key='SQLArchiveConnectionString'][@value='Data Source=WIN-A52S8EPVOT4;Initial Catalog=TRAEmployee;User ID=sa;Password=P@ssw0rd;Persist Security Info=False;']";
            myModification.Sequence = 0;
            myModification.Owner = "administrator";
            myModification.Type = SPWebConfigModification.SPWebConfigModificationType.EnsureChildNode;
            myModification.Value = "<add key='SQLArchiveConnectionString' value='Data Source=WIN-A52S8EPVOT4;Initial Catalog=TRAEmployee;User ID=sa;Password=P@ssw0rd;Persist Security Info=False;' />";
            web.Site.WebApplication.WebConfigModifications.Add(myModification);
            
            service.Update();
            service.ApplyWebConfigModifications();
        }

is there any suggestion for my problem ?

your reply will greatly help me to finish this problem

Regards,

Jay