Update X-Forwarded-For in C# Code

I need help updating the X-Forwarded-For header in our current .NET Framework desktop application.

Requirements:
- Modify existing C# code to correctly set or update the X-Forwarded-For header.
- Ensure changes do not disrupt existing functionality.
- Provide documentation for the changes made.

Ideal Skills:
- Strong experience with C# and .NET Framework.
- Familiarity with networking concepts and HTTP headers.
- Good documentation skills.