When you go to install RS, I'd pick to do it manually, not let the install configure. Then, you'll have the option of walking through each part of the config yourself using the config tool after the install is done. When you get to the database step, you can tell it to use your existing db and not have to create a new one. This would save you having to restore the backup.
Of course, having a backup is a great idea, just in case, and if you do need to restore it, it will bring back any of the security settings you've already configured.