rFactor knows that the files are there because is defined in the "searchpath" lines in .gen , and the game will look for objects there and if they are present they will overwrite the included in .mas files.
the fisrt digit of genstring very often in the mod is used to define the headlights, that number 1,2,3.... defines where rfactor have to look for objects, luces1 luces2 luces3..... folders.
you can add your custom wheels there , make a new folder , (lucesx) put your wheels and headlight objects there and in your .veh put one "x" in the first digit of genstring , that wheels will be loaded instead of the present in .mas files
remember to rename the materials of the new wheels and the new textures !!!
now ,you guys know another way to include new wheels to the mod without making changes in .gen or .mas files