Settings overrides are a way for extensions to override selected Chrome settings. The API is available on Windows in all current versions of Chrome and is available on Mac in Chrome 56 and later.

Homepage, Search Provider, and Startup Pages
Here is an example how homepage, search provider and startup pages can be modified in the extension manifest. Web sites used in the settings API must be verified (via Webmaster Tools) as being associated with that item in the Chrome Web Store. Note that if you verify ownership for a domain (for example, http://example.com) you can use any subdomain or page (for example, http://app.example.com or http://example.com/page.html) within your extension.

For external extensions, the search_provider, homepage and startup_pages URL values can be parametrized using a registry key. A new registry entry should be created next to the "update_url" key (see instructions here). The value name is "install_parameter", the value data is an arbitrary string:

MORE HERE: https://developer.chrome.com/extensions/settings_override

Custom default search engines soon possible?