Change Windows 8.1 Metro Search Provider
Solution 1:
I've asked this Gov Maharaj from Microsoft and I got the answer that is it not possible. There are no registry keys you can edit to change the search engine. You can only turn it off.
Watch one of the next episodes, he should answer it there.
Solution 2:
Sure, you can always to do it for Internet Explorer or another internet browser, but Microsoft isn't going to let about half of its Bing traffic go to waste, and frankly, I don't blame them. Until someone manages to hack the system or release a workaround, I don't think there's anyway to switch it. You can, however, go to the Windows store and get the Metro/Modern app for Google or your other preferred search engine, and that could make it easier to search the web from the start screen.