Today if we were to keep developing the car, we would add fender vents to relieve pressure in the wheel wells, add more pressure reducing vents to the hood. add extensions to the side skirts to reduce air from spilling under the car. Make some improvements in underbody air flow. Lower the ride height and add some front to rear rake.
Any of the things we did here can be easily made in the home workshop and if you follow our guidelines will absolutely help, not cause excessive drag, possibly reduce it nor screw up your aerodynamic balance. Going more radical than this can mean some cut and try possibly going backward. Unless you have access to analytical tools like CFD or can hire an aerodynamicist with motorsports experience, our mods are safe and sure. Go ahead and try them on your car!