Professional
VST PlugIns and
AU PlugIns

How do I save a preset in the plugin?  If I click the save button it saves to a file.  I would like to modify a preset & save it with the same name or even save it with a new name.  I see how to type over the name of the preset, but that changes the actual preset that I start with so it only really helps if I start with the 'Default' preset or something from the "ROM" so I can load it back in again.

You may create a new bank in the preset manager and then save the preset as many times as necessary - simply use the "+" button and then give a name to the preset.  It does not require file storage.