Set clockspeed of Arduino Pro Micro a. k. a. AtMega32u4
Absolutely. The built-in prescaler can dynamically change the clock speed for most of the systems on the chip (USB still needs to run at full speed in order to operate properly).

#include &lt;avr/power.h&gt;

 ...
clock_prescale_set(clock_div_32);
sleep();
clock_prescale_set(clock_div_1);
 ...


See the datasheet and AVR Libc documentation for more details.