Python Add-In: Modifying an existing add-in?

Hopefully I am just overlooking the obvious here, but how do I go back to modify an add-in? I used the Add-In Wizard (addin_assistant.exe) to create the original, but now I want to add additional controls (tools, combobox, etc..).

That particular wizard seems to only be for creating the add-in.

Thanks for any help!
j