Okay, there are multiple things at play here.
First, if you want to add additional parameters to the 'out of the box' start parts, you will need to manually open those cad models, add the parameter, and then save them back to the same directory. There are located in the <loadpoint>\templates directory. Most people don't bother with this but instead build their own templates, store them somewhere else, and then point Creo to these folders/models instead (as Steve mentioned).
Second, if you create a parameter and you want it to automatically show up in the list when create a new part from it, you have to designate it. Simply check the box next to the parameter in the designate column.
