Go to File>Preferences and check the box saying: Allow negative real values in the Object Editor. Then go to the OE, select your doodad and set Max Roll Angle (degrees) to a negative value. Do the same with Maximum Pitch Angle (degrees) if you want. If it doesn't allow you to enter negative values, hold shift while opening the field.
-3.14 rotates the doodad by 180 degrees, -1.57 rotates it by 90 degrees and -0.79 rotates it by 45 degrees. The doodad might be buried in the ground after rotating, so you might need to raise it (Ctrl+PageUp).