Yeah, a partially broken board if the best place to "play" with this sort of thing. Unfortunately, the TQFP package is a major PIA. I haven't attempted it yet, but I suspect a SMD rework heat gun, insolated gloves and tweezers will be involved.
I heard of many 16u2 failures on the Mega2560 and always wondered why the Unos were unaffected. Not the case apparently.
Good luck.