Accept File Extension Changes in OS X with Command-U Keystroke
When you go to change the file extension in Mac OS X you will get a dialog box notifying you that by changing a file type it may open in another application. Chances are if you are changing the file extension deliberately, you did this intentionally and the warning is not necessary, but it’s shown just in case.
That’s ok though, because a keystroke expedites the process. You can quickly accept this file type extension change by using a simple keyboard shortcut that’s pretty easy to remember:
Just hitting Command+U when the dialogue box pops up instantly accepts the file extension change.
You can try this yourself, but you’ll need file extensions to be shown in the Mac Finder.
This appears to be a feature added to OS X after Snow Leopard only, but I do not have access to an older Mac OS X to test. It does work in OS X Yosemite and Mavericks, however, so the feature is likely to carry forward from future releases of Mac software.
Finally, it’s worth mentioning that if you really don’t like that dialog box, you can actually disable the extension change warning by using a defaults command string or system setting.
Another great trick is to enable the tab key dialog box selection option, which lets you tab between active elements on screen.