I haven’t started the project yet but I’m going to be testing the airflow over a car while I add individual parts and tweak them to get the results I want. I’ll start with the base car, test it, then I’m going to add a rear diffuser, test it, then add a front splitter, etc… I was just wondering if there’s a way I can quickly and easily run the test after I add each part or if I have to redo everything for each separate test?
Hi, this is Fillia 
You can copy a simulation, and change the geometry. The settings will remain intact, however you will have to reassign them to your new geometry.
By the way, make sure to check the vehicle tutorial to help you with your project: Aerodynamic Flow Behavior Around a Vehicle Tutorial | SimScale
Best regards,
Fillia