Change file type descriptions in Windows 7

• Launch regedit.

  

• In HKEY_CLASSES_ROOT, find your extension (you just have to type .qtz). Example with .ods file:

  

• Look for the Data of the (Default) value (in my case, opendocument.CalcDocument.1, but in yours, something related to your application), and find this name in HKEY_CLASSES_ROOT again, by typing the first letters. Example with opendocument.CalcDocument.1:

  

• Change the Data of the (Default) value to the description you want.

  

• Close regedit.

To see your changes appear, you can either reboot, or change the default association of some file by choosing "Open with > Choose default program..." (I couldn't find the proper method). Here is the result:

You can also use NirSoft's GUI-based FileTypesMan utility. It's available for both 32- and 64-bit systems.

• Use Ctrl+F or Edit -> Find to find your file type
  • Searches by any field available. See the Edit File Type dialog below.
    • Include the . for faster extension searches, such as .script
• Edit properties as desired.
• Toggle advanced options as desired.
• Click OK.

Pretty great, flexible, and very easy.

References

• NirSoft's File Types Manager for Windows page
• SevenForums' Windows 7: File Extension Icon - Change Default Icon tutorial

The solution proposed by m4573r used to be the only way to do this up to Windows XP but doesn't always work in Windows 7 if file extensions are first associated with a program from Explorer (when using "Open with >").

In such cases you might have to navigate to the following registry key:

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts

and change the (Default) value directly under your file extension registry key.