It's difficult to do this because you have to create a form that edits the database. You can accidentally do a self-injection if you used a funny character in one of your custom codes.
BUT if you insist on being able to view and edit codes, it's not too hard if you wanna do it manually. Be warned that if you mess up the database, you WILL have to redo everything. This means a bunch of useless codes if you never backed them up.
1.) Go into your web host contol panel. You're going to want to go into the MYSQL settings.
2.) Get into PHPMyadmin
3.) Look for your WordPress database (click on databases until you find one with "wp_" as a prefix on all the tables
4.) Look for wp_DCR_codes
5.) Click Browse
6.) Here are your codes. You may edit them as they aren't hash encrypted. If you export this CSV, edit the codes column in excel, and import using "replace values" then you can do the codes manually.
Complex, but possible. Good luck, and don't mess up your database. ALWAYS BACK UP!