I don’t know this for sure, but I’d assume if the changes are material, you can change it. For what it’s worth, I do know (as I recently did it) that you can SDS/SDC on web special awards.
That is a great deal though... Far better than the 26k I just spent on a DFW-BOS one way LOL (though the cash fare was $500+ so it’s not as bad in that context).