You can replace a circuit breaking without turning off the main breaker...the same way you can reach into the oven and grab a pan without a potholder. Working on a circuit breaker without turning off the power is taking your life into your own hands. \
Turn off the electricity before you start doing any electrical work or you could be making a fatal mistake. It is extremely dangerous to work on a circuit breaker without turning off the electricity and it's important to remember that even though something is possible, that does not mean it should ever be done. \