Removing or Editing File Associations through the Windows 7/8 registry

The registry is an incredibly sensitive file that contains a vast amount of highly unorganized data in the form of folders and keys.  My patience was really tested when a user decided to open a special file extension in MS word.  Now the file's properties displays an undesired program as the default.  Also, I've seen people try to open a file but the program doesn't open properly signifying that the parameters are incorrect.  If anyone has made this mistake before and would like to resolve it, I have some instructions and places to look.
I will be using the file extension ".ext" as an example for the steps below"

First, everyone should know about the "default programs" section in control panel.  Unfortunately, it doesn't paint the whole picture.

In command prompt, type "assoc .ext".  This will display the name of a program that it is associated with this extension.  This data comes from the "classroot" section in the registry.

Also in command prompt, type "ftype nameofprogram".  The "nameofprogram" is taken from the output of the command "assoc .ext".  This will display the command used to describe the behavior about how the file is opened.  Normally you will have a %1 next to it letting you know that it is taking in the file that is associated with it as a parameter.

If you don't get any clues from above and need to go deeper, then here is where the registry comes in.

***BACKUP THE REGISTRY BEFORE MODIFYING THE REGISTRY***

There are numerous places to look for a misbehaving file extension, all are taken from this very well written article:
 http://www.mydigitallife.info/how-to-unassociate-remove-or-delete-programs-from-open-with-or-recommended-programs-list/

The following places to look are:

HKEY_CURRENT_USER\Software\Microsoft\Windows\
CurrentVersion\Explorer\FileExts\.<extension>\OpenWithList

HKEY_CURRENT_USER\Software\Microsoft\Windows\
CurrentVersion\Explorer\FileExts\.<extension>\OpenWithProgIDs

HKEY_CLASSES_ROOT\.<extension>\OpenWithList

HKEY_CLASSES_ROOT\.<extension>\OpenWithProgIDs

HKEY_LOCAL_MACHINE\SOFTWARE\Clients\<Program Type>\
<Program Name>\Capabilities\FileAssociations

HKEY_CLASSES_ROOT\Applications\<application executable name>\SupportedTypes

HKEY_CLASSES_ROOT\SystemFileAssociations\<Perceived Type>\OpenWithList
HKEY_CLASSES_ROOT\SystemFileAssociations\.<extension>\OpenWithList

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths

The most popular one would be this: HKEY_CURRENT_USER\Software\Microsoft\Windows\
CurrentVersion\Explorer\FileExts\.<extension>\OpenWithList

Remove the OpenWithList should fix the default "Open With" program listed in the file's properties.

If a file is not opening properly or if you're crafty and would like to modify how your specific program opens, this is in the "classroot" section of the registry.  This section will also modify this for every user of the computer, not just yourself.
HKEY_CLASSES_ROOT\.<application name>\Shell\Open\Command
Then edit the (default) key data.

Remember, every time you edit the registry, restarting the explorer.exe process doesn't always work as it depends on where you edit the registry that would be taking effect.  For all of the above, save yourself the headache and just reboot the computer.