Hello,
Yes you can, for example if you take the "google.php" file located in the modules/mod search folder you will notice two lines that control what search engine is used.
<iframe id="s5frame" name="s5iframe" src ="http://www.google.com/search?hl=&q=" width="100%" height="300px" frameborder="0">
and
document.all.s5frame.src="http://www.google.com/search?hl=&q=" +delineate(text);
You would have to change these and replace with whatever search engine you want to use.
Regards,