./launcher start app
Should do it, unless the database has migrated, in which case you can have problems.
If you want to revert to an old version and then restore your backup, you can delete the postgres_data directory, change tests-passed to the version you want (either the beta or an actual commit) and then restore the data.
I’m confused about your permissions issue. I haven’t done an upgrade, but I did a couple installs today and they worked fine.