This is Pandoras Box!!!!
If you have a "car", repair portions of the "car", you still have the "car". If that "car" were a GTX, it would still be a GTX.
If I purchased a Sat, and placed GTX badges on it, it would not turn into a GTX... It was not sold as a GTX option car.
I fall into the category of folks who believe if you "Re-Body" a car, it's not longer the same car. If I repair portions of the body, it still holds it's "same car status".
Now you ask, "how much of the car can be repaired before it's no longer concidered "the same car". Well,,,, I dont know for sure.... For me, I would think anything beyond new quarters and fenders, perhaps doors too... This is something that you as an owner or potential purchaser have to conclude for yourself....