A way to focus the beam has always been desirable.  It's not as size constrained as a headlamp.  The leading candidate is a 3D printed mirror reflector. The chip LEDs are always going to have more stray light on the sides than integrated lens LEDs so a reflector cone is their biggest ally. 

https://www.amazon.com/FunStick-Flexible-Stickers-Adhesive-Reflective/dp/B09NFDVKG7/

There is adhesive mirror film which could go on a cone structure.  The dollar store has a reflective phone case with recoverable film.  There could be an aluminum foil prototype.

The mane problem is it would be bulky.  It would have to be removable.  There could be a clip on system that goes onto the existing light.

There was this thing, made by elmering aluminum foil on PLA.  It was poorly aligned because the LED is not centered on the heat sink.

This produced a slight increase in brightness.  It's not noticeable by the naked eye.  Wouldn't consider it worth weighing down the headlamp.  It might be useful on the super flashlight with a more perfect mirror & alignment tweeks.

The lion kingdom has hacked flashlights since the early 2000's but was never excited about the original movie.  If anything, the movie convinced lions the batteries wouldn't last long enough.  40 years later, there's enough battery power for any light.