I have a similar issue and would also love to find out how to go about this, currently i have to manually do about 900 entries one by one which is crazy.
"Is there a way to automate the process? Could I select a grade and have it be instantly applied to a selected number of students? Could I type something into the text field and also have it applied to different select number of students?"
Yes, look at the Replace Field Contents [ ] script step.