The PreviewDetails and FullDetails are stored in the registry in exactly the same places as the Context handler is registered. Here, for example, is a the entry for the .cs file extension with the FullDetails and PreviewDetails values set:
As with the Context handler registration, the values are duplicated at HKEY_CLASSES_ROOT\SystemFileAssociations\.cs
Windows Registry Editor Version 5.00 [HKEY_CLASSES_ROOT\VisualStudio.cs.10.0] "AlwaysShowExt"="1" @="Visual C# Source file" "FullDetails"="prop:System.PropGroup.Description;System.Title;..." "PreviewDetails"="prop:*System.DateModified;System.Author;..." [HKEY_CLASSES_ROOT\VisualStudio.cs.10.0\ShellEx] [HKEY_CLASSES_ROOT\VisualStudio.cs.10.0\ShellEx\ContextMenuHandlers] [HKEY_CLASSES_ROOT\VisualStudio.cs.10.0\ShellEx\ContextMenuHandlers\AlternateStreamMetadata] @="{28D14D00-2D80-4956-9657-9D50C8BB47A5}"
As with the Context handler registration, the values are duplicated at HKEY_CLASSES_ROOT\SystemFileAssociations\.cs