Opera desktop team has released Opera 26 by replacing Bing with DuckDuckGo, since this browser doesn’t allow to make custom search engines as the default ones due to security reasons, I suggest you to don’t create one, that is a waste of time, but still, you can add Bing back and set it as a default search engine in Opera, here is how.
Setting Bing as default Search engine in Opera 26
1. First, navigate to C:\Program Files\Opera\26.0.1656.60\resources and backup ‘default_partner_content.json’ file to another location on your hard drive.
2. Now download this file having the same name and paste it in the resources subdirectory (which we’ve mentioned above), when Windows shows a copy file dialog, select ‘Copy and Replace’.
3. Now launch Opera, open Settings, click on ‘Manage Search Engines’, you’ll now see Bing in the default Search engines, hover over it and click on ‘Make Default’, done.
4. To get DuckDuckGo back, you need to paste the file we backed up earlier in the resources folder again.