In a typical case, if you use a certificate to book a trip and want to cancel or change date, there will be a change fee. If this certificate is used on an EXP, such change or cancellation fee will be waived.

If the trip is canceled, the certificate itself becomes available for booking (to a different itinerary or even a different individual), but it remains a certificate with expiration and rules associated with it.

If you want to redeposit the certificate back to the points (so that you can redeem for a different product), then there is a redeposit fee. The certificate itself belongs to the small business, not an individual, so the conversion of certificate back to points won't be associated with any AA status and thus no fee can be waived.