Hi JGAnderson,
My apologies for the delayed reply! I see you have a few posts here which Ill be getting around to at some point today, so keep an eye out for me responses :)
To answer your question - If you are looking to add new values into a DropDown - you are going to need to create a new screen based off this dropdown (complete with all relevant fields, save button etc).
A Dropdown is essentially a Link to another Table, albeit typically a very simple one. Every value in the dropdown represents one record in the Table, similar to how you have a list of Contacts in your Contacts table, for example.
A Good reference for how we handle DropDown record addition in Method Stock Apps would be to take a look at the New Activity Screen. Take a look at the Type Priority, or Status fields, (and its actions) to see how we handle this without needing to navigate away from the screen.
Thanks JGAnderson
-Ben