Please make sure to finish all your posts before this time. The downtime should only last for a few minutes.
You'll find Presto-based Opera (v12 and earlier) to be the last ones with good configuration and customization options. Everything after it is based on Blink (a.k.a. Chromium, a.k.a. Chrome), which has minimal customization choices. Even the proxy settings now are limited to the OS settings, no internal proxy function at all.
It's a different theory in Opera 20. In general customization is through extension. Most users didn't use customization features built into the old Opera. Not all the features of Opera Presto can be replicated that way, but new ones can be had, via extension, that never were possible.
Instead of using Opera:Config try using this instead opera://flags/