How to spoof a web response header/code in C++?

This is my first post so please let me know if anything is wrong with this post.

Anyway, the question here is that I'm trying to find a way to spoof a web response header/code in C++. I've tried using LibCurl to find a way to do this but couldn't figure out how. Is there any other way to do this? I know I could use fiddler to do it, but I want to make my own http response modifier.