How many times you had press F2 for renaming a file and had missed extensions ? This is very common and windows should have this feature which prevents users from changing the extension type. Well one way is to never show the extensions of your file making it a lot better when you rename and still preserve the file type or Time time for another utility.
TheEnd is another small utility by same guy who wrote Create Shortcut There and it deselects the Extension automatically when you press f2 or rename.
This utility doesnt need any installation but it keeps running in the background. You can have it on startup and save lot of hassles when you rename. Download TheEnd