A few questions:

Discount codes (such as Baggage service guarantee) cannot be combined with % off discount codes (such as for a wedding or event), correct?

Are the new fare guarantee issued as discount codes, or as certificates for my wallet?

As MVPG I am allowed to change reservations, or cancel reservations without fees. What if I change or cancel a reservation for which I used a $$ off discount code? I have a $175 discount code from previous fare difference that is nearing expiration; was planning on using it, but my plans aren't final. I am too used to the MVPG benefit of changing...but don't want to cancel this itin and then have the $175 value completely forfeited.