I am trying to develop a chrome extension that would set the "host" header on certain requests. But the documentation is contradicting as to if the "host" header can be modified or not. 

Both of these issues indicate that a) it should not be possible and b) it is impossible
<https://code.google.com/p/chromium/issues/detail?id=154900>
<https://code.google.com/p/chromium/issues/detail?id=158073>

Yet multiple extensions in the gallery state they do modify the "host" header.
e.g.
<https://chrome.google.com/webstore/detail/header-hacker/phnffahgegfkcobeaapbenpmdnkifigc?hl=en>
<https://chrome.google.com/webstore/detail/change-http-request-heade/ppmibgfeefcglejjlpeihfdimbkfbbnm>

Is it possible to modify the "host" header in the windows version of chrome, and if so how?

Background: I want to be able to test load balanced web instances hitting each host directly via ip address. The "hosts" file is to cumbersome for a large number of hosts. At the moment I use curl to pass the modified "host" header, but I really need the solution in the browser and available for others.