Changing value on appSettings webconfig. Only works on second pageload

Question

I have below code running. Changing an appSetting in my webconfig. But I have to make a extra pageload to "make the magic".

1st. pageload. uses previous setting. second pageload. Okay.

I have it placed inside Page_PreInit :

    Configuration configuration = WebConfigurationManager.OpenWebConfiguration("~");
    AppSettingsSection appSettings = (AppSettingsSection)configuration.GetSection("appSettings");

    appSettings.Settings["FileManager"].Value = "newValue";
    configuration.Save();

Answer 1

If you mean the codes that run after This code by "first page load" this is something normal.

Config file just lunches after a request . 午餐。
i think the only solution is making that extra page load.