Certainly.

>> If so, would the cutout be centerd over the rectangle where the
>> original port would have been?

Yes, you could do it that way.

>> Its no big deal if not possible, but thought I'd check to see if
>> there was any particular reason why the port was rectangle.

Here's the big problem. It won't fit. The Stage Series, Premium Series and Professional Series four π Speakers are all such a tight fit, that the rectangular port is required just to get the layout to work. And honestly, I think it looks cool that way.