UKAzzer published a video to YouTube (via Reddit) that shows him playing around in the game's debug mode.
From there, he was able to edit the highways that connect cities together outside of the city boundaries. The game's city sizes have been criticised by some for being too small.
"You can edit the highways ANYWHERE - even outside of your city boundary," UKAzzer said, "and even if you quit the game and log back in later, it's all saved safely on the server.
"This shows that highway editing will be easily possible, AND that editing outside of the artificially small city boundaries should be very viable too."
Meanwhile, UKAzzer modded out the "fluffed population count" so the game shows the real population count - a disparity players have complained about since launch.
Most importantly, UKAzzer was able to disable SimCity's disconnection timer, thus setting it to unlimited. Tests have shown SimCity kicks you out after around 20 minutes of offline play.