There is no difference between "original" and "restore" keys.
Once Media Center is licensed on a PC, it remains licensed until you do something that breaks the licensing, generally, but probably not limited to, changing the name of your system or reinstalling windows.
When you use the licensing system to generate a restore key for yourself, it is just that restore key that is valid for 14 days. That means that you have 14 days in which to use it to register Media Center on your PC, after which, the
restore key file expires, and if you need to restore again after that, you would need to get the online system to generate another restore key for you, which would again only be valid for 14 days.
The system allows you 10 restores in 12 calendar months. You should realistically never run out, but if you do, let JRiver know the whys and wherefores about it and they will typically, erm, restore your restores
