Hi @operabop, you can change the UA by adding the --user-agent switch at the end of the shortcut to the launcher.exe, for example:
"path\to\the\launcher.exe" --user-agent="Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/45.0.2454.93 Safari/537.36"
Alternatively, if you want to set the UA for temporary use (it only persists, while you have the Dev Tools window open), copy your custom UA string, and press Ctrl+Shift+I (opens the Dev Tools), press Ctrl+Shift+M (toggles Device Mode), and on the right of "UA" click on "No override", paste the UA string (Ctrl+V, or right-click on the field, and select "Paste" from the context menu)
Is there a way to set a popup dialog to get permission before downloading/updating like Firefox or Adobe flash?
According to the official Opera help website, the autoupdate option settings is available under the Preferencs settings. But I can't find that setting any more.
Those instructions are for Opera Presto (Opera 12.17 and older).