Why can't read the CLKPR register?

Projects Programming
4

You have to set the CLKPCE bit before you can change the lower bits. If you DO succeed in setting the low order two bits, your prescale will be 8 and your Serial will suddenly be 1200 baud instead of 9600. Maybe you can change the baud rate to 76800 right after you change the prescale so you can receive the text at 9600 baud.

void setup() {
  Serial.begin(9600);

  delay(1000);
  
  Serial.print("CLKPR Before:");
  Serial.println(CLKPR);
  CLKPR = 1<<CLKPCE;
  CLKPR = 3;
  Serial.begin(76800);
  Serial.print("CLKPR After:");
  Serial.println(CLKPR);
}

void loop() { }