I had this same question today. I'm updating a layered image and testing in my app. I make little tweaks and see what it looks like in my app. I see the 3 step solution, that includes jumping between mouse and keyboard, but it would be more efficient if I had a single step. Especially given I've done this 5 times in the last 20 minutes.
One simple solution could be an "export" or "Save copy as" menu option, that remembers your last save format. Ideally a single keystroke mapped to this option two would increase my productivity with this great app.
btw, is there a place to vote for features?