Hello.

You will need to do some customization to accomplish this task.

At first, you need to clone existing Newsletter subscription web part since you will modify its code. You can clone web part in Site Manager -> Development -> Web parts -> select web part, clicking Clone web part button.

First task is make redirection to second page (containing cloned web part) after user subscribes to some newsletter. You can do it in code-behind of /CMSWebParts/Newsletters/NewsletterSubscriptionWebPart.ascx.cs web part, in „Submit button handler.“ You can use UrlHelper.Redirect(string url) method for this purpose.

On second page, cloned Newsletter subscription web part is placed. If you need to add new fields, you can add them as standard .NET controls (asp:TextBox). In code-behind, you need to ensure that new values are saved into proper columns (sb.SetValue() method).

Best Regards,
Radek Macalik