There are two different modules that allow you to edit fields within Blackbaud Grantmaking (formerly GIFTS Online). 

The first, is the Blueprint module. Here, you can create custom fields and add and remove existing fields on your records.Any custom fields created can also be used on an application form. The below link has more information on the Blueprint module:
https://www.blackbaud.com/files/support/howto/coveo/gifts-online/go-mod-blueprint.html

The Classifications table is where all coding fields are stored. These are fields that usually show up in the "Coding Sheet" section of a record and have values associated with them that can be selected. These fields offer the option to click "Edit Codes" when present on an Application form. The below link has more information on Classifications.
https://www.blackbaud.com/files/support/howto/coveo/gifts-online/go-core-codetables.html