Yes, you can add additional funds to your CD during the grace period from an existing Third Federal savings or checking account.
To do so go through the "Additional Services" tab in online banking. Select "CD Maintenance", then the CD that you would like to renew/add to. In the drop-down select the option to add additional funds, select the account and dollar amount you would like to add.
You can also enter the CD Maintenance page through our Mobile App by selecting the "More" option after logging into the app and then select "CD Maintenance".