It is safe to install an electric switch yourself as long as the power is off. Making sure the power is off is crucial and is done by turning off the breaker or turning off the main power.
Breaker panels are often labeled to identify which area each breaker supplies power to. Once the appropriate breaker is turned off, test the area to confirm that the power source is truly off. In extreme cases, such as when breaker panels are not clearly labeled or when testing an area yields uncertain results, turning off the main power is necessary to completely ensure that power to the area is off. This method, however, eliminates access to power outlets for tools and light.