NOTE: This feature is currently in beta. The server IP below will change when the beta ends.
As discussed [here][1], Safari doesn’t allow you to customize the search engines available from the search bar.
However, there is a simple hack you can do. DuckDuckGo operates a server that can respond to Safari’s 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.
Method 1: Mac app