Requestly founder here! If you're still looking for a solution to modify HTTP Headers [0], you can try Requestly - An Open-source[1] Chrome & Firefox extension to intercept & modify network requests.

Although Requestly is a freemium product, the free plan offers unlimited HTTP header modifications. You can get Requestly here[2]

[0]: https://requestly.io/blog/modify-headers-in-https-requests-a...

[1]: https://github.com/requestly/requestly/

[2]: https://chrome.google.com/webstore/detail/requestly-redirect...