There have been a lot of posts on this subject recently. Some say yes, others think there is a safety margin. There are few if any, reported cases of bikes 'snapping in half' with riders on them, but there are plenty of cases where bicycles of the heavy develop failures or cracks around the seat-tube area, where the seat post clamp is. If you're tall with it, there's more leverage too.

If you're on the limit, you're on the limit. No amount of magic-wand waving or metaphysical belief will fix that.