How would I modify a shortcut that had been created using the INUIAddVoiceShortcutViewController?

I am creating an iOS app using Xcode and Swift that uses INShortcut. After the user has created a shortcut based on a user activity using the INUIAddVoiceShortcutViewController, how would I modify the shortcut or actually the user activity in the shortcut using code without showing a user interface and update the shortcut?