This is essentially the Android version of the Windows Registry Editor. It's invaluable if you need it, but if you're not careful you're very likely to mess something up.
By default, for your protection, Android prevents you from modifying the SECURE and GLOBAL tables. If you have Android Jellybean or later, you can remove this protection from an ADB shell using the command "pm grant by4a.setedit android.permission.WRITE_SECURE_SETTINGS". On earlier versions, you can only remove this protection on a rooted device by installing Settings Database Editor to the system partition.