Reversing the switch is easy, most of those type of switches have a clip on the bottom that can be removed. Once removed, you take the float off of the center post and flip it upside down.
One word of warning, that switch is rated for 20 watts, that is why they are so cheap. I was using one that was rated for 30 watts with an Aquaclear 401 pump and damaged the contacts so that the pump was "stuck" in the on position. Wiring a second switch as a shutoff switch will work to prevent overflows though. Also, some people put the whole topoff system on a timer so that it only can run a couple of times a day, this is a second back up method. Just be sure your pump isn't overdrawing the switch...I've since been told that maxi-jet pumps have a lower start up current draw...this is what damages the switch, a high start up current. When the pump receives the power it draws more current to get started then what the operating current on the box is posted as being. Good Luck!