You could copy the profile directory over (you will lose existing preferences from Opera beta, but you'll copy over everything from Opera 43).
Make sure both Opera and Opera beta are not running.
Then run these commands from a terminal (minus the '$' at the start):
$ mv ~/Library/Application\ Support/com.operasoftware.OperaNext ~/Library/Application\ Support/com.operasoftware.OperaNextBackup
$ cp -R ~/Library/Application\ Support/com.operasoftware.Opera ~/Library/Application\ Support/com.operasoftware.OperaNext
Now start Opera beta and it should have your Opera 43 profile 🙂
