Well you can Edit/Undo (ctrl+Z) immediately, but if you're past your undo
limit then I'm afraid you can't (other than to close the document without
saving and then re-open back to a previous saved version). When carrying
out certain Shape/Operations Visio creates a new shape so you may be left
with very different shape geometry.
Sorry the news isn't good.
Best regards
John
John Goldsmith
www.visualSignals.co.uk