To duplicate the condition, you could:
* Go to the grader report in the gradebook
* Click the button in the top right "Turn editing on"
* Enter grades
* To save, click the update button
You can also remove your overridden grades by clicking the edit icon for the item in this page, and unselect "overridden".
As in my previous comment, I would not suggest you use overridden grades for assignments, but it is helpful for quizzes and other graded activities where you can not enter grades directly when students submit them in ways other than Moodle.