Am I correct about that?
No, you are about as incorrect as it is possible to be.
First, you have no function "exitSafeStsrt();" defined, so the compiler will complain.
Second, assuming it was a typo, and meant to be "exitSafeStart();", you still haven't given it a value for "device", so you will still get the compiler complaining, though about something different.
You can default the value of "device" (though the Arduino may not like the some placements of the definition), which allows you to omit the value of "device":
void exitSafeStart(uint8_t device = 0) //if you omit the argument, it will default to whatever value you specify here
{
mySerial.print(NEWCMD, BYTE);
mySerial.print(device, BYTE);
mySerial.print(EXITSAFESTART, BYTE);
}