If you are going to launch the coin first, the  it might be better to do it as a spin-off coin rather than directly in Nxt.
Or alternatively, you will need approval from users.

 It changes the inflation model. Holders of USD units of value are able to print 1 USD worth of Nxt. This means that the aggregate supply of Nxt fluctuates with the Nxt/USD exchange rate. That is a pretty substantial change.