Turn off the settings to display the helmet, and the MOD can be replaced. Turn on the helmet and turn it off directly.
The method of replacing MOD: find the Model.vac file in the gamedata folder of the game directory manager and unlock it with CM3DExtractor.exe program. Just put the Model.vac file on it. You don't need to unzip to the same folder. If you unzip it directly in gamedata, you will get a folder of Model. You only need to copy the files in the replacement shelf to the unlocked mode folder. That's it. Some files that need to be unlocked are the same.