For all, who want to get rid of the default serach engine (Google) forced by Opera Mobile, here's a hack to achieve this:

1. edit file /opt/operamobile/browser/bream/skin-vga.rsc (probably not on your phone!)
   • seach for "Google" an replace this string with your favorite search engine. But the new description must have the same length (i.e. 6 chars), if shorter fill with space (0x20)
   • change the following URL
     Code:

     http://www.google.com/m?q=%s&client=ms-opera-mobile&channel=new

     according to your favorite search engine, e.g.
     Code:

     https://duckduckgo.com/?q=%s

     %s is of course the search string. Again, keep the original length by filling with spaces. Btw. the "duck" has a really big advantage, you can define (start page -> more -> settings) the color scheme to dark, which gets saved in a cookie.
   • deactivate Google livesearch by replacing
     Code:

     http://clients1.google.com/complete/search?client=opera-mobile&hl=#{locale}&q=#{query}

     with
     Code:

     http://127.0.0.1/disabled_google_live_search______________________#{locale}&q=#{query}

2. delete ~/.config/operamobile-labs/ds/8_all. The file get's regenerated out of skin-vgs.rsc upon starting opera. But be aware: You will loose all added custom search engines! This work has to be done once again afterwards.
3. add the following lines to your /etc/hosts:
   
   Code:

   127.0.0.1  server1.operamini.com server2.operamini.com server3.operamini.com
   127.0.0.1  server4.operamini.com server5.operamini.com server6.operamini.com
   127.0.0.1  server7.operamini.com server8.operamini.com server9.operamini.com

   That's necessary, because Opera checks on every start for new default search engines and will undo your efforts within seconds. Again a drawback: You won't be able to use Opera Link anymore!

I didn't bother to cahnge the Icon -- you'll still have the (old) one of Google.

Hope you enjoy this little "trick"

Read original German version in my blogpost.

EDIT: The path given above refers to the Harmattan version of Opera Mobile 12; for Fremantle edit /opt/opera/share/browser/skin-vga-multi.rsc and delete ~/.opera/ds/8_all