In case of invens and item frms I don't think the naming extensions have a lot to do exept they show which are the similars ones. The settings that will determine what can you do with that item is set in the mapper so its quite different thn the heads and critters.
Here is a pic that may help you (oh and don't forget to set your mapper to create the proto files)
Here is a pic that may help you (oh and don't forget to set your mapper to create the proto files)
