If the rubber is new and the corners are crisp and even, I would leave it. The reason to break the corners is to match the sides, it will also change the way your plunge grinds, as mentioned above. If you don't like the way the sharp edge plunges come out, then consider breaking the edges. This has been done for 30+ years, it was much more common in years past, but it's still a fine thing to do if you need the plunge or you have an untrue wheel.