So if you try and do this on the Nitrado Interface on your server page you get an error. here is how I done it.
Step 1: Shutdown your server
Step 2: Select Config Files on the left hand side of the interface
Step 3: At the top you will see a green box that says load file, if you click on the black box beside that (default seems to be Users.eco) you can then select Difficulty.eco
Step 4: Change "PlayerExperiencePerSpecialtyExperience" to the value of 0.0
Step 5: Click the save changes button at the bottom.
Step 6: Start the server
Step 7: Have Fun
I hope this is the answer you were looking for.