For your adidas fantasy car, i built a tool to be able to rename cars and patch the .gp4 file to use new textures.
Its name is Livery Editor (clic on the banner below to get it)
So just copy the original .gp4 used by your fantasy car and rename it as the arrows file (or make gp4 use any new name for the car, ie:adidas) and rename your adidas .gp4 file to that name with LE (Livery Editor).
Then if you duplicated an original shape to put in the arrows' slot, you will have to change textures used by the .gp4 files, else you will have 2 times the same car.
My tools has been designed to patch a .gp4 file and make it using any prefixed name for texture.
That way you can use a car named car_Adidas_lod_0.gp4 with textures named hi_adidas1.tex, hi_adidas2.tex and hi_adidas3.tex.
have a good try.