Optional Accessories or Objects for a Car Skin - eg Spoilers

[BJ911]

I want to create a single car model with optional accessories, such as spoilers, grilles etc. for different skins within that model. I want to avoid making different models depicting those different items. I am aware it can be done for individual skins, by using different KN5 files containing those additional objects, and creating an "ext_config. ini" file for that skin. The code in that file contains a "MODEL_REPLACEMENT" line, and an "INSERT" line, but I have no idea how to code the rest of the file. I haven't been able to find a sample car model that I can use as a guide. Any help would be appreciated.