It is possible to change voltage level to 3,3V, however this puts microcontroller outside its specifications. The microcontroller is clocked at 16MHZ and according to the datasheet microcontroller should be powered from 5V with this clock frequency. I did not have problems running the microcontroller at 3,3V and 16MHZ, but it is not a reliable and recommended solution. Also, when running microcontroller at 3,3V you have to make sure that you do not connect 5V level signals to it.
Yes