You don't need to change your download region, because the files you get are determined by what edition of the game you own, not where you download it from. To get an international key from Humble Bundle, you need to use an IP address that isn't associated with Germany or other countries that censor a particular game. You can do that via proxies or, better yet, asking a friend from another country to gift you the Bundle. Using a proxy may not help if you pay with a German credit card, though.
The key itself determines whether you get a censored version or not, though some games might provide additional complications - being unable to activate them or download an activated game while in Germany or other country with mad censorship laws - that sort of thing is normally noted on a game's Steam store page under the screenshot slider.
Source: I've been gifted a Humble Bundle copy of Titan Quest that was bought in Germany, and had to spend a month arguing with Steam Support to get them to remove the game so I could redeem my international key for that game.