Is it possible to save and run your levels on hard or easy? Or is there a mod or something?

I dont think there is any way to do that via JCS. The fastest way to run your levels fast with any difficulty setting is with the utility Captain Cook.

Arg, bummer

You can make a .bat file or use cmd to make JJ2 load a level with your desired difficulty:

Jazz2 levelname.j2l -easy/medium/hard

Leaving the difficulty argument out will make JJ2 load it at medium difficulty by default. The full list of JJ2 command-line arguments is found here.

Maybe in a future realease of a new JCS, we will have that option on JCS to chose *hard
*medium
*easy
______________________________
but what white rabbit say is true....that is the best way to chose dificulty.