Dear @Roberto.Echeverria.
The way of specifying a downwind rotor has not changed…it is still done by changing the sign of OverHang, etc.
FAST / OpenFAST can only model wind turbines rotating in the clockwise direction (when looking downwind). For more information, see my response to a similar question in my post dated Feb '13 in the following forum topic: Coordinate System in FAST - #9 by Neelabh.Gupta.
Best regards,