I am not suggesting any change from the format as it is, just the addition on +1 or -1 buttons to change the values. As for the restriction section, I suggest the addition of the calendar options as found in further up in the form to set due times/dates.
It might be that others are not finding it all that much of a problem. Depending on my assignments, I might be making 20 changes/assignment, almost 70 assignments per course and up to two courses being at least 10 hours to make the 2800 updates for each semester.
These little changes for selecting values would go a long way to making it much more tolerabler.