Sigh, here we go again...
It's unlikely an LED in place of an incandescent will meet the requirements.
For one thing, the lens, and any reflector inside, are designed around the exact location of the filament. An LED doesn't have a filament, and the light will be coming from different locations and at different angles.
For another, the light wavelength won't be the same, so the red and green lenses on side lights may produce an odd (and out-of-spec) color.
The point is not that the CG is going to board you and take your fixtures apart. The point is that (1) you won't be legal, maybe even not safe, and (2) if there is an accident, and you are found to have non-conforming lighting, you will be found at least partially responsible. I've heard of a number of cases like this; two where some drunk in a go-fast ran over someone at night, and the drunk's lawyer challenged whether the boat they hit was properly lit. Apparently it's a common tactic.
Finally, in the overall cost of owning a boat, the price of a good, purpose-built, sealed LED fixture is small potatoes. In my experience, it's often the fixture and not bulb which fails in the salt air anyway. Just buy the right LED fixture and be done with it.
