BuddyPress.org

BuddyPress RC2 will consolidate your activity streams and merge the tables. It will also go through and add any additional settings that are missing and set them as default if for some reason they do not already exist.

As long as you have not hacked the core of your install, upgrading from RC1 to RC2 should not harm any of your existing data.

There is a built in maintenance mode when using the automatic update feature of WordPress, but for something manual (such as RC1 to RC2), I might recommend something like…

https://wordpress.org/extend/plugins/maintenance-mode/