There are two changes that Code Jam team have just announced.
The first change is that it is now possible to upsolve this year's problems. To do this, you need to be logged in. Open any past problem and press the "switch to practice mode" button at the top right. Practice mode will be available 24/7 except during official Code Jam rounds. There is also a site-wide limit of 10 submits within any 10 minute window.
The second change is that it is now possible to view and download other participant's code after the contest. To do this, click on the participant's nick in the scoreboard.