registering custom file icons in carbon

let me preface this by saying, this is NOT related to the application icon. i have that working by adding my .icns file to the resource folder and setting the 'icon file' property under the default target's properties page.

so to clarify what i do want: i have a custom proprietary image type that i want to create an icon for. once this icon is created, how do i 'register' it with the os so that it shows up for my .xyz images in finder? in my info.plist, i have a CFBundleDocumentTypes entry where i specify the details of this file type using CFBundleTypeName, CFBundleTypeIconFile, LSItemContentTypes, etc... so do i need to do anything else beyond this?

also, i noticed when photoshop's .psd icon isn't displayed as a scaled-down thumbnail of it's respective image, it uses a generic image icon shared by jpeg, png, bmp, etc. file types - with, of course, the textual part at the bottom spelling out the file extension. how did adobe accomplish this? does the mac just recognize psd's, or did adobe take get that generic icon and just put textual 'PSD' in it and package the custom .icns file with their app?