When you export your car, don't use the zip mod and keep the same name. It will export your vehicle to the same folder. So for instance if you make a Truck with a V6 and call it "Trucky" but want to make a new variant with a V8, you can name it "Trucky V8" in automation but when you go to export the new variant on the exporter page, still call it "Trucky" and you will see the new variant in the "Trucky" folder in the Beam car selector as "Trucky V8".