I hope this is in the right spot. When it comes to changing website content based on visitor location, serving targeted ads and content...in theory, could this not be applied to single individuals online? For instance, you normally use CNN. Say you wanted to serve a completely different reality to a handful of individuals without them recognizing the stories they're seeing don't completely match to the actual stories most people see...based on their exact location on the grid, down to the individual user level? I'm not suggesting this has any practical or real-world benefits, it's more just a general inquiry.
If the content is Geo location specific, you can redirect after determining source address to that Geo location specific content. Same way, if you can categorize specific user based on whatever factors, you can show content based on category. You just have to define category buckets and put users into it, and define content for specific category bucket.
Potentially the same as "A/B" testing where a group is given a different version of a site and their clicks/purchases/other behaviour are monitored and if they do more of what the site owner wants their version will eventually go live. I suspect that for big news sites you'll see a different version depending on whether you're in the USA or not. Adult sites too, probably. With geo-location, if the difference is permanent, you should change some of the heading tags to reflect the location - then Google will know that someone who searches in Country A will get the Country A version.