The Chrome browser (and others like Edge) allows you to override both HTTP response headers and the response content. I've previously written about overriding the headers for testing purposes, let's see how you can override the body, or the content itself, as well. Starting with Chrome 117 (released in September 2023) it's also greatly simplified.
Starting with Chrome 113 (and in other browsers like Edge), you can override HTTP response headers, or add a new one. This is handy as you can override e.g. some security headers for testing. The HTTP response header override will be applied before things like CSP are processed so you can modify the Content Security Policy for the page for example.