Disable File Extension Warning
If you often find yourself changing file extensions, you might be tired of the annoying "Are you sure you want to change the extension..." dialog box. For example I often end up changing the extensions of text files from .txt to .html.
Luckily, you can disable this warning quite easily. Just go to the Finder Preferences (under the Finder menu in the top left) and click on the Advanced tab. In here, un-check the checkbox "Show warning before changing an extension".
Now whenever you change a file extension, you won't be presented with an "Are you sure" warning.