I would like to add a preview video to an app that is "ready to sell". The documentation seems to suggest that a new binary version needs to be created. I have no changes to the app binary. Can I use the current app and create a new version with the added preview mirror or must I go back to Xcode to create a new version although nothing has changed?
App preview video
You will need to submit a new binary with the new version number. That's the only thing that must be changed.
You'll need to go thru a normal update submittal routine, again, to add a Preview - just bump the version number in the current build, generate a fresh archive and go again. Call it a 'minor change' if you want to provide info why.