Any of the presets that come with Studio Artist can be edited to customize the effects they create.
To do this after loading a preset in the Preset Browser, go to the Editor. The Editor will contain a series of control panels that make available all of the different editable parameters associated with the particular effects you are working with.
Some effects may only have a few editable parameters in one control panel, while others like Paint Synthesizer Presets have a vast range of different editable parameters located in a series of control panels in the Editor accessed via a popup menu at the top of the Editor.
When you change any of the parameters associated with a preset file, the changes are not saved in the actual preset file unless you specify that specifically.
If you are editing an existing preset and you want your changes to overwrite what is stored in the current preset file, you can do that by option clicking the current preset icon in the Preset Browser. A dialog will come up asking you if you want to overwrite, and press Yes if you do.
If you want to save your editing changes as a new preset file, then you can use the appropriate File : Export menu for the specific kind of effect you are working with.
Saving your changes as a new preset file allows you to still keep the old original effect around as well as your new edited changed effect. That way you can access them both at a later time.
File import and export menus are also available via contextual menu shortcuts when in the Editor or Preset Browser.
On a mac, you control click to get to contextual menus for whatever part of the interface you clicked on. On windows, you right click.