90 degree turn - lets say you wanted to lay a column on its side, in the object editor Art - Max Roll or Art Maximum pitch (just one of these) hold down shift and double click, then enter -1.57
That number lays doodads down on their side. Mind most doodads end up halve buried in the ground, you will need to select the doodad and while holding Ctrl use the page up key this will raise it, page down lowers it.
To completely turn a doodad on its head, lets say you want to use stalagmites as stalactites for a cave scene, select one or the other of pitch or roll and enter -3.14
Unfortunately doodads will have their 'base' at ground level, thus you will most likely not see it, you will have to select it and raise it up.