I'd say best practice at the moment would be to make a note/screenshots of your old app settings just in case so you can manually set things up later. You can swipe down on the "Sync for Reddit shutting down" message in the old app to hide it and still get into your old settings. That said, the current test version can restore from an old backup, but it breaks some stuff like preventing comments from loading. From what I saw while recreating my settings everything seemed to be there 1 to 1 so it shouldn't be too bad.