A script would be a good way to go about that, but it would need to be written specifically for what you're trying to do, I think. I'm not sure if there are any generic search scripts out there that do something like that.
You could use an extension like
Context Menu Search, which allows you to add searches with whatever search engines/parameters you like to the right click menu in Chrome. You could set up a new search with
https://www.google.com/search?q=TESTSEARCH+USA as the search link, where TESTSEARCH would be your variable and USA would be your constant. So you could highlight anything, right click, and have a search option in the context menu to search for that word + "USA."
It's not the most efficient solution, but it's at least pretty quick and easy to set up if you're not familiar with any scripting languages.