Not easily. I've tried. Many trips to Radio Shack, hours of research, and about $30 worth of bulbs, batteries etc. later, I finally ended up sticking with the original bulb.
I was having a really hard time matching the bulb with the right battery (that fit in the flashlight). At one point I did have a 6v LED setup (or something close), and a 6v battery setup that fit in the flashlight, but you had to go into a pitch black room to see the faint flicker of light.
Then again, I can't claim to be a professional regarding flashlights and bulbs, but I did read a lot and the end result wasn't very promising.