Thanks for your reply. Unfortunately like I stated this messes up the filename, since "undo" doesn't undo the filename which has been selected for the Save As, which really makes this... well... not that much of a pseudo-export.
I understand that you cannot give a definite confirmation about the addition of this function but I would like to stress that IMO this should really be in the top range of the todo list... This is really a pivotal function in ANY multi-layer graphics program. In fact you'd be hard-pressed to find one which doesn't have it ;-)
You see, A LOT if not most Paint.net users export their multi-layer source graphics to JPG/PNG/BMP/GIF since well, PDN is a nice format but not very useful outside paint.net itself so it's not like it would be a hardly used niche-feature that only a handful of webdesigners and programmers would benefit from. It is seemingly not an incredibly hard feature to add either I'd imagine or would it?