other way that im testing is using a legit DLC car as a donor car. (scion fr-s 12) im test with subaru BRZ disguised in a scion fr-s. and other BRZ in a premium subaru body. the second car receive a (!) sign after using them offline and online (the car name also changes when i select them) but the car in the fr-s body still fine after selecting in home garage and using offline and online, the car name never change always appears like Scion fr-s. when you choose a car by maker it appears from scion (the subaru BRZ appears in scion maker)
How to select the car from your home garage

read carefully)
-select a scion fr-s as a donor car
-using the garage editor and create your DLC/stealth/chromeline car
-once in the ingame garage use triangle button, and never the cross button
-select your car from the menu
sorry about my stinky english