How can I make Roland GS the default patch list?
I'm not sure if there is a way to directly do that,however, there is an option you could use. Make a template for your scores with the Roland patch set under staff properties. If you use the standard templates, just open each, change the patch under staff properties and do a "save as" to the templates folder. Then start all of your new files by opening through the templates. This would give you the type of function you're looking for.