I want to modify rewrite rule from C# code. Url Rewrite rule is resides in web.config file.
Microsoft has Microsoft.Web.Administration.dll available to help you out, but it requires administrator permissions to execute,
https://www.iis.net/learn/manage/scripting/how-to-use-microsoftwebadministration
It is quite suitable for a WinForms application (such as IIS Manager) to control an IIS server, but can also be used in other types of applications.
I do have a personal project that is a custom MWA implementation that works for some non-administrator cases. If you are interested in it, let me know.