MacOS – Change the default Icons OS X 10.4.11 Tiger

There is a cute bash script that converts your aliases into symlinks, which sounds like your best bet honestly. Aliases aren't useful for much really.

This isn't an answer but it does add some information. The value associated with the com.apple.LSSharedFileList.TemplateSystemSelector key, 1935819875, is a decimal representation of the file type. In hex, it is 0x73624463, which are the ascii letters 'sbDc'. This file type is described in /System/Library/CoreServices/CoreTypes.bundle/Contents/Info.plist. This is a binary plist that you can convert to xml using plutil -convert xml1 -o Info.plist.xml Info.plist. Looking in the Info.plist.xml file, you can see a dictionary at the top level. Inside this there is a key "CFBundleDocumentTypes" and an array of dictionaries as its value. In this array is a dictionary that contains the following:

<dict>
    <key>CFBundleTypeIconFile</key>
    <string>SidebarDocumentsFolder.icns</string>
    <key>CFBundleTypeName</key>
    <string>Sidebar Documents Folder Icon</string>
    <key>CFBundleTypeOSTypes</key>
    <array>
        <string>sbDc</string>
    </array>
    <key>CFBundleTypeRole</key>
    <string>None</string>
    <key>LSTypeIsPackage</key>
    <false/>
    <key>NSPersistentStoreTypeKey</key>
    <string>Binary</string>
</dict>

An interesting key/value pair in this dictionary is CFBundleTypeIconFile: SidebarDocumentsFolder.icns. This file can be found at /System/Library/CoreServices/CoreTypes.bundle/Contents/Resources/SidebarDocumentsFolder.icns and it contains the icons used for document folders.

I would think that changing the com.apple.LSSharedFileList.TemplateSystemSelector value to a different value, or updating the dictionary for 'sbDc' to refer to a different icns file would get you on your way to having custom icons.