I created a part file template with specific file properties under a different name (not the original solidworks parts).
When I create a new room I have the properties already pre-filled).
But when I create a new part from an assembly, it is the default part model that is created, I then lose all my pre-filled fields in the properties, or should I change, in the soptions I presume but I don't see or exactly.
Otherwise, once you've changed your part and its properties to make a default model, all you have to do is save it as a model where all Solidworks model parts are saved. (I don't remember the extension though)
So, when you make a new part, you will have the choice between the default Solidworks part and your default part. All you have to do is choose;)