Yes. Any electronic document, including unused tickets, may be used towards the amount due when changing your itinerary online.
Yes, on wholly domestic itineraries only.
Some types of eCredits are transferable, please refer to the Terms & Conditions for the specific eCredit. To transfer an eCredit to someone else, you'll need to provide them with the original 13 digit voucher number, complete name as it is printed on the voucher receipt and redemption code when applicable. Paper vouchers must be transferred in person at a Delta ticket counter or Ticket Office Location.
Passengers with disabilities have priority seating, which results in the occasional need to change an assigned seat, with bulkhead seats being particularly subject to reassignment. We appreciate your cooperation in these special circumstances.