Yes, you can change a grade category in a grade plan after you have performed the rolled over, as long as there are no grades recorded using the grade plan. To do so:
 

1. Go to Academics > Grades > Grading Setup > School Year Setup
2. Filter for the School Level and Grade Plan Group the grade plan is in
3. Click the View button
4. Click view for the grade plan you wish to edit
5. Click the Edit button
6. Click the Category drop down for the grade plan grade you wish to change it for
7. Set it to the desired category
8. Click Save & Exit