In general, the voltage rating of "passive" components like switches and connectors is their max rating, and lower voltages may be used with no difficulty. (In this case the rating is basically for the insulation within the switch, and the distances between bare metal components at different voltages. Staying within the rating assures that the insulation will not "break down" due to voltage stress and that arcing between parts of the switch will not occur.)
There are two separate concerns, however, unrelated to the voltage rating. First off, one must keep the current through the switch below its max current rating. Your switch has a half-amp rating, so you need to keep current below that level. Most uses for signal and control applications don't exceed a few milliamps, but if you are, say, powering a motor you could see higher currents.
Secondly, arcing. When the switch "breaks" (turns off) and the contacts in it pull apart, it's possible for there to be an arc formed between the contacts, causing them to briefly heat up and be damaged, and, in rare cases, causing the current to continue even when the switch is supposedly off. This is mainly a problem with "inductive" loads -- relays, solenoids, motors, etc. If you are switching such loads you need to study up a bit on how to deal with this situation.