Normally it is that easy... But with downgrading 3.16 to 3.13 two things happen. 1, you will only be left with system package once it boots into 3.13 unless you upload individual packages to downgrade to (disaster if trying to downgrade from wireless). 2, any files that were on the hard disk that * disappeared* with the upgrade to 3.16 will be still gone after your downgrade back to 3.13.
Keep tryin' its bound to work!!
ROOT@COSMOS> Reality.sys corrupted -- Reboot Universe (Y/N)?