As a piano rebuilder, I can tell you that the problem is the difference between the actions (the collection of parts that translates the key movement to the strings) in a grand and an upright. The grand action has what is called a repetition lever, which the upright does not have. It allows for rapid repeating of a single note. In a piano that new it is probably as quick as it will ever be right now. As to the movement of the hammers, the position of the hammers is part of the design of the scale of the piano. If you move the hammers closer to the strings, you will loose some of the power of the piano, and will not gain any speed. It will also affect the touch. If I were you, I would save that $450.00 toward a baby grand. You can find some good deals if you take your time.
Thanks, George