Every time you change a files extension, for example from .jpg to .png, or .avi to .mp4 your Mac will give you are warning. This is so you don’t cause anything untoward from happening. If you have changed a file extension, the program will try and open that file extension. For instance if you change a .avi to .jpg Preview will try and open it and fail. This can cause you a bit bother since you have to force it to open in your video app. It stop this from happening your Mac gives you a warning. However, I find it annoying since it is an extra click to change a file extension. Most of the time I know that I am changing a files extension.
Removing The Warning
Removing the warning is very simple. It is a built in preference within Finder.
Open Finder and go to Finder > Preferences. From the options select the advance tab. The magic option ‘Show Warning Before Changing An Extension’ needs to be unchecked. When you uncheck this option the warning will never appear again.
It is obvious when you find it. I can never find it, these options are either in some preferences or system preferences. I always pick the wrong one.
You can us a terminal command to do the same thing. It is longer, more complicated and does exactly the same thing as the method just posted. To use a Terminal command, open up Terminal in Applications > Utilities.
Type the following command and hit enter.
defaults write com.apple.finder FXEnableExtensionChangeWarning -bool false;
To revert the command use the following
defaults write com.apple.finder FXEnableExtensionChangeWarning -bool true;
I prefer the check box method.