You can't pass a game save between profiles (I assume you mean Gamertags), since each save is tied into the profile.
You can't pass liveries. What you can do is sell them from one profile to another through the storefront. Both profiles need Xbox Live Gold to do this, though.
And no, saved liveries only can be used on the car you "saved" them. What you can do is save each part of the livery (left side, right side, roof, bumpers, spoiler) as a layer group, then put each layer group into the new car.