If you enable and use the console, you can change difficulty with the command "setdifficulty #" where # is a number between 0 and 3, from easy to elite.
To enable the console, open the settings.txt file located in My Documents/My Games/Runic Games/Torchlight 2/Save
Then scroll down until you see CONSOLE: 0, and change the 0 to a 1.
To open the console ingame, press CTRL+SHIFT+NUMPAD_0.
If you use the console, it flags your character as a console user. Other players online will be able to see a mark next to your portrait. If you don't care about this, go ahead, otherwise I'd stick to just remaking LAN games and changing the difficulty there.