Some people use black trim. You can find it on Amazon.
You do have to CUT & DRILL your car's fenders. While you could easily replace your front fenders the backs aren't really repairable.
If you paint match the fender flares, the trim you are looking for keeps the flares from blending in and looking factory.
Rust is not a problem if you prep/prime/ paint properly. Also that "as seen on TV" Flexseal works as a great undercoat. But if you travel on gravel you should recoat when you swap brake pads or rotate tires.
I have the full HT Autos kit, paint matched, on my '16WRX. And I still get people video taping me on the highway every other week.....it was daily the first couple of years. I think they look naked without them now.
The best, but most costly option would be to get a VIN off a S209 and order replacements from Subaru. About $3K in parts b4 paint n body. They look a bit nicer.
If you decide to cut your car hit me up. I can give you some great install tips.