That might be slightly true in a V8 or V12 engine that's been run at max rpm on a race track. But driving a little four cyclinder Toyota around? There's no way that's going to be an issue.
I don’t think Prius and other Toyotas in the US have them as far as I know. In any case, it is illegal to tamper with any kind of emissions systems, not to mention that the car will fail the emissions inspection or test.