The fact is that no aircraft is certified to fly into FZDZ or FZRA, being it light or moderate or severe. During certification, the aircraft is certified to fly through freezing precipitation up to a droplet size of 50 microns. FZDZ starts at 200 microns and FZRA 500 microns. Those 2 conditions are known to be associated to SLD (supercooled large droplets), which will freeze immediately after coming into contact with the aircraft.
The term light or moderate has nothing to do with the droplet size but with the number of drops...and that's what a lot of pilots forget.
As well, it is also not always related to the outside air temperature. Talking about freezing precipitations, we are talking about the droplet temperature, which in those cases would be below 0 degres. So sometimes you can get freezing precipitations with temperatures being even slightly above 0 degres.