The original collision file needs to be retained too, or it becomes more than just a cosmetic mod.
The car crash just after 0:08 in your video is followed abruptly by your losing connection to the server. I can't help but think this is due to some kind of server / client data mismatch caused by your modded vehicle. Although I would have expected that to result in a ' game crash', so I could be wrong about that.
Either way, the first sentence in my post is a LW's server requirement.