Unless you have are replacing an HD DVR its not possible. Dish does have the ability to connect an External USB2 Hard Drive to either a 622, 722, or 722k. You do have to pay a one time fee to use the feature on your account. Once you pay the Fee you can use as many External Hard Drives you wish on any 622, 722, 722k on your account, you can also take the same External Hard drive and connect it to any other 622, 722, 722k on your account.
If you wish to save content you already recorded to any other Dish DVR 501,508, 510, 522, 625 and reload that content on to a replacement DVR you are SOL.