To be completely fair, if he'd promised anyone except Aziraphale, there's only a fifty-fifty chance he'd have actually kept his word. But he can't deny the angel anything. One of Crowley's curses.

"Yeah, that's all right, then," he says. "Work on it a bit every day, drink a bit afterwards. Give me something to make sure Aziraphale doesn't stay on the docks all night long. And he would, if you let him. He shouldn't be feeling as guilty as he is."

Shapeshift the wings, though. Crowley can shapeshift into a snake, do a bit of shapeshifting to scare people, but nothing as intense as moving his wings around the way it sounds like she can. Such an odd bunch they have in this town.