On 9.0 beta 2, I have tried to prevent autostart of the database engine via
the by the process shown in
Leaving the file in place and setting the <key>RunAtLoad</key> to <false/>
does not seem to have any effect.
The only method that I have found to work is to remove
the com.edb.launchd.postgresql-x.x.plist file from the LaunchDaemons
directory. But I would prefer to leave it in place, and change as needed.