urlfilter.ini for Opera Mini For Opera or Opera Mobile it's possible to block certain URLs by adding a file urlfilter.ini to the user profiles. On Opera Mobile this file would be placed at /data/data/com.opera.browser/opera/profiles/smartphone/urlfilter.ini.

But this approach only seems to work for Opera Mobile, not Opera Mini. Is there a way to block certain URLs in Opera Mini so that the normal user can't change it via the Opera UI? 

Another idea I had (my app runs on rooted devices with secured su access) but which wouldn't entire cover all my requirements:
Modifying the /etc/hosts file and change all urls to 127.0.0.1 - but the problem is that I don't just filter entire domains, but also just certain suffixes, etc. *.apk, and /etc/hosts doesn't allow wild cards just for file suffixes.
I don't think this line of thinking would work. The Opera Mini experience is built on the premise of the client being able to connect to Opera's rendering server farms and having a web page that's optimised for mobile view being sent to your phone/device after being compressed in order to save data network costs.

I don't think modifying your hosts file would work on Opera Mini - Mobile and your default browser - yes, because they connect directly from your phone to the page you're trying to view.