Led's
I agree with Rick D I don't think the USCG is going around checking light bulbs on working navigation lights and no reputable insurer is going to deny a claim on such basis.
Benny that has never, ever even been a concern of mine. My concern, and there is much case law that shows nav lights do come into play in court cases, is the lawyers will turn this into a blood sport if you are involved in a night time collision, whether your fault or not, and eat you for lunch. Unfortunately the burden becomes yours to prove proper beam width, intensity and color and without a proper certified light that will be expensive and difficult.
My friend Kim's father was killed on a large lake in NH and the nav lights under went forensics testing to determine if the stern light was actually on at the time of the accident or off. The nav lights alone were almost two days of testimony.
It was determined through forensics that it was on but nav lights were a huge part of the case. If Kim's dad had been using an after market LED it's entirely possible the drunk who hit them at 40 knots, and killed her dad, may have got zero time in jail even though he was the one at fault..
With after market LED's it''s not the insurance companies or the USCG you need to worry about it's James Sokolove....

Think it does not happen it impacted me and someone I knew very, very well. here's a direct quote from the court docs.
State of NH vs. DJL said:
During the post-collision forensic investigation, Maurice Boudreau, a consultant with the State Police forensics laboratory, examined the stern light. He testified that the light was still operable, but that the lamp filament showed signs of "mild hot shock," or distortion.
This means the filament was on and hot enough to stretch due to the impact. If it was off there would have been no stretching and instead it would have just fractured..
If you are going to switch to LED's for nav lights it is a good idea to use LED fixtures that have been sold as LED nav lights and that are certified. Orca Green Marine, LopoLight, Hella and others do make them and they are USCG/COLREG certified for beam width, color and intensity.
While it is rare that an acciddent would happen, like a drunk driving incident, it can happen and does happen. As I've become older I have less of the "it won't happen to me" attitude and more of the "it could happen to me" as life experiences have shown the latter to be more true..
Remember the USCG is not checking up on you but the lawyers are the big bad wolf!!