Cook macaroni as directed on package. Drain and return to pot; keep warm. While macaroni cooks, in a medium saucepan melt the light butter with canola oil over medium heat. Stir the flour into the butter. Whisk in the milk all at once. Cook and stir until milk is thickened and bubbly. Cook 1 minute more. Remove the pan from the heat and add the cheese; stir until smooth. Stir in the yogurt. Add sauce to macaroni and stir to combine.
Stir in cooked shrimp and Cajun seasoning just before serving.