This is possible with hex editing of the savegame file and is relatively simple to do. You need to make a copy of the file and then in the game normally change the spoiler of the car you want to mod with any other spoiler and save it. Then you need to go to your hex editor software (I use hxd) and use the compare function to find the change between the the modded and the original files. Once you identify it (iirc it’s 4 hex values) you can overwrite it with zeros, save and there you go