var oRoot = Application.ActiveProject.ActiveScene.Root;

var oCube = oRoot.AddGeometry("Cube","MeshSurface", "CubeParent");

var oTrans = oCube.Kinematics.Local.Transform;

var oRot = XSIMath.CreateRotation();

oRot.SetFromXYZAnglesValues( 0, XSIMath.DegreesToRadians( 45 ), XSIMath.DegreesToRadians( 45 ) );

oTrans.SetRotation( oRot );		

oCube.Kinematics.Local.Transform = oTrans;