Is it permanent?

hi, i’m new to arduino and programming and couldn’t bring myself to play with the pwm frequencies without asking first
If i change them using this method http://arduino.cc/playground/Code/PwmFrequency
does it leave them like this even if i upload a new sketch? or is it specific to the sketch that uses that code. Is it permanent or reversible?

Is it permanent or reversible?

Only for the duration of that sketch.