Also, an update:
Just received the following message from Frontier. Has anyone actually tried to change flights and has either received or not received a credit when using the Works package? Customer service response seems to contradict the website (original post).
Thank you for contacting Frontier Airlines Customer Relations regarding The Works package.
If a scenario where this would be needed, if you just email me back, I would be more than glad to help you out and issue you a credit for the fare difference.
For Future Frontier Flights
Below are some links for of our bundled packages, The Works and The Perks. Each option bundles extra services such as bags and seats, in one low price.