You can import Gradebook .csv export files back into Canvas after making appropriate edits. In order to import your .CSV file into your Gradebook in Canvas, first navigate to your course site's Grades page. From here, click on the Actions button in the upper left of the screen. Then, select Import.
This will take you to the Upload Gradebook screen. Click Browse... to find the desired .csv file on your device. Once you have selected that file, select the Upload Data button in order to begin the import process.