To make edits or add a note to this section, you will need to follow these steps: 
1) Open the grant in question, and go to the Application History tab, and then the Payment Plan supertab. 
2) Find the adjustment in question, highlight it, and right click on it and select "adjust grant".
3) This pulls up the Adjustments screen, and you can then edit the reason for adjustment.  
4) Then process the adjustment, and it will then update your comment in the reason for adjustment textbox. 

NOTE: This same process is also applicable for Scholarship Adjustments.