Note that WD changed the “roll back” FAQ on 12/21/12, and it describes what the new restrictions are regarding roll back of Live and Live Plus units:
How to roll back the firmware on a WD TV Live HD Media Player or WD TV Live Plus HD Media Player This answer explains how to rollback (revert to a previous version) the firmware on a WD TV Live (WDBAAx0000NBK) HD Media Player or WD TV Live Plus HD Media Player device. Answer ID: 5800 | Date Updated: 12/21/2012