:))) Oh well.
Now, if you are going to keep the browser open all day, follow the procedure I outlined. It's a few simple clicks, and then you can type from the main address bar, without using the code letter, and you will have that new default engine, until you close the browser. So you'd have to go to Tools > Preferences > Search. Highlight the engine you want as default while the browser is open -- let's say DuckDuckGo -- and then go to Edit > Details > put a check in Use as Default Search Engine.
But linuxmint7 is right. It only works while the browser is open. Once you close it and open it again, what you've changed is lost. Sorry there. I thought I had made a discovery.
Looking at the bright side of things, by following the procedure I recommended on getting rid of the Google Search bar from the Speed Dial, you have succeeding in hiding it. When I closed and opened Opera 12.17, and went to the Speed Dial page, the Google Search bar was gone.