Change Management - Adding an option to the Planning stage?

Hello! I am working on tweaking our Change Management workflow, and I need to add a specific field to the planning stage for a specific form that needs to be done for each RFC at our company. Currently, the options in the Planning stage are Impact, Roll Out Plan, Backout Plan, Check List, and Downtime. I want to simply add another option there for this form which would can function exactly like these other options (with and "Edit" and "Attach a file" options). I cannot find a place within the Change Workflow to edit this list or add to it in any way.

Is this possible? Please advise on what the best route might be for adding a static field on all of our RFC's for a company-specific form. Thanks!

Zach