Harmy said:
OK, there will be some cases, where going back to the original files and re-rendering won't be an option anymore - in those cases, would you prefer I
A) Keep the corners just in those shots
B) Crop the corners out by zooming the shots in a bit
C) Try to paint them out invisibly (that is the option I'm personally leaning towards)
Option C, especially if it's the one you're already leaning towards.