If you're using Mac: In the future, please keep in mind that you don't need to delete a machine when you reformat your hard drive or update your system. Our servers will still be able to recognize that you’re using the same computer, so you can reauthorize it without wasting an authorization. Also, keep in mind that if the same machine is deactivated more than once, it will not be counted again. But if you do frequently need to move your authorizations to unique consoles/computers, please consider keeping at least one of your three authorizations on a flash drive (instructions below).
If you're using Windows: You generally don't need to delete a machine when you reformat your hard drive. However, there are certain settings changes you can make on Windows (like bios settings) that will change your machine ID. So if you find that your PA plugins don't recognize your computer after you make changes, please consider keeping at least one of your three authorizations on a flash drive. Then you can freely change any settings or even use different consoles/computers without worry of running out of deletions again.
How to keep an authorization on a usb stick: (This procedure can be done on any computer with an internet connection and the plugins installed. It doesn't need to be the computer/console that you plan to use your plugins on.) Make sure your usb drive is in your computer. Then, open one of your plugins in ProTools (or any host) and click the key icon on the bottom right side of the plugin window. An authorization window will pop up. Under the text "Select the device you would like to activate" there is a pulldown menu. Click it and select your USB drive. Make sure the "Activate all my licenses" checkbox is checked. Then click "I'm Online" and enter your login info, and click "activate." Now your USB drive is authorized and can be used on any computer.
One more thing, in case you didn't know: There's almost never any need to individually deactivate your plugins one at a time. Normally, you can just go to Manage Devices and there you'll see a list of your authorized machines, and a "Deactivate" button that removes all the authorizations from a machine all at once. It will make your life a lot easier if you frequently upgrade systems.