...does this mean I can replace my O2 sensor with a wideband...[/b]
With the new rule? Yes.
...if not, is the addition of a wideband legal?[/b]
It is currently legal to install a wideband under the "additional gauges" (you're installing an AFR gauge) but it is not currently legal to replace the stock narrow-band O2 sensor as an input to the current ECU.