The Lancer Evo. VI TME can have the normal Evo VI front bumper and taillights. Kinda a reverse on what you can do with the Evo. VI GSR in Forza.
Just in case you didn't know, you can do a license plate delete. Though only on the front bumper sadly.
The Evo. V GSR can have its foglights covered, like on the Rally Car. It also has flared wheel arches for a widebody kit, so you can recreate the rally car for the most part.
Like the Evo. VI, it too can have its taillights altered for if you wanted it to look like the RS version I guess or the Mine's Evo V.
The Subaru Impreza Type R can have a less agressive bodykit, I'm guessing more like the 1998 Type R.
It also has alternate spoilers similar to the earlier STIs or the WRX models. Something to keep in mind if you wanted a more normal looking Impreza.
the Porsche 964 Carrera RS has a spoiler like on the Turbo S and one like on the 1970s Carrera RS. Sadly no custom wings available.