Hi sneather, once you have your styles set up how you want, save that to a 3DM file and then make that 3DM file the startup template file under Options > General > "Template file".

When you specify a template file, it will be read at startup and File > New to populate file-specific things like the styles list.

If you open some other file and want to bring in your default styles list into that opened file, there's a menu item on the Styles section of the Scene Browser called "Add default styles" that will do that.

- Michael