I know my opinion is not the most popular on this topics.
The is a reason why we have a standard pattern on how to name textures of tracks and specially of cars. To avoid mismatchs. Renaming from 011 to 011x is just a matter of time until the next mismatch. Also I recon the other textures have equally random names? If I am correct BTB has this sort of name output in some cases (bloody annoying if you look for a file in a track sometimes). So why not name it,as in any good mod: number_type_maker_body1.dds and it is easy to have an overview for everyone?

Renaming a dds is quite straightforward. If you have SimEd3D you use this. Simple but not Freeware. If you don't have it you can rename with Geditor and a Hexeditor. Extract with Geditor, rename, import with Geditor. But keep in mind that the number of signs in the file name remain the same. So 011.dds to xyz.dds is ok, to 011x.dds not ok (in this case. If you use SimEd3D you can do whatever you want). Then open all GMT files in the Hexeditor and change the name as you changed the file names. You can usually use "search and change all" function. Then include all gmts and textures in the Gtl files and use the trace to find gmt files you maybe forgot to change. This way pretty much ALL additional wheels for add on cars were made in the early gtl/gtr days (when 75% of all the skins were painted for the original cars).
Hope it helps.