Do you want to work more than the 475 hours that you get from the government?
You can, but then you pay the normal social security contributions.
Once you have reached your quota of 475 hours, you owe normal social security contributions starting from the 476th hour worked.
Please note: even after reaching your 475 hours, you remain a student and you must therefore have a student agreement. The only difference lies in the amount of social contribution that you pay.