To be honest, there's not much of an advantage using a K&N.

It will get clogged up quickly if it's muddy and doesn't really stop the water getting in if there are puddles on the track.

You're right, the original air box will act as a snorkle and it is possible to modify the filter inside the airbox to flow better. The airbox itself only has four tiny holes to let the air in, so modify that to let more air through but keep the water and dirt out.