Lets say you have a Document Set, with a Web Part on it's Welcome Page. Let's say it has some custom settings (like a list name that it interacts with). Can you edit those settings like you would a web part placed on a normal page? Would/could you do this from any particular item's welcome page? Or is there some special way to access the generic "welcome page" for the content type?
The pages are aspx files and can be accessed either using the Browser or Using SharePoint Designer.
If using browser you can use Site Actions -> Edit Page. And then either add/edit the web parts that are available on the pages.