Modify hosts file to make DuckDuckGo replace Yahoo Search
duck.co/help/desktop/hosts-file
From the page
Saved with the link. Notes from 2007 to 2016 are mostly the page's own words, so this is probably an excerpt.
DuckDuckGo operates a server that can respond to Safaris search requests directed at Yahoo, Google, or Bing, and send those to DuckDuckGo instead. To use it, you can either use an app to make the change, or edit your hosts file directly.