I want to add a function for the Denon AVR-985; I want a button (LCD button) to increase the center channel volume and another to decrease the volume.

When I go into learn commands menu, it lists these 2 commands but does not state that they are in the database (does that mean that the ones that are listed as in the database will automatically work?). I have the IR code from the Denon website (101011 for level up and 011011 for volume down). Where (which menu and how do I get there) can I enter these codes so that my Harmony One will be able to perform them?

This is important as I do not have the remote to learn the command.

Did you try the commands that are already there in Device mode to see if they work? If they do then just map them to a button. Support can add pronto hex codes but not the binary codes you listed.

Unfortunately, those commands are not options in the device mode or else I would have simply mapped them onto a different button.

Try a similar model like the AVR-888. The dataset for the Denon AVR-888 contains these Center Level commands (and also the Back level commands). Add this model to your configuration to try these commands (in device mode). If they work, then ask support to copy them over to your AVR-985 model. Or, use the AVR-888 model instead if its dataset has all the desired AVR-985 functions.