If I remember right, the LED for the Maglite Mini is in a pill that is pressed into the barrel, and can be pressed out by pushing from the rear. I’m not 100% certain on that, however, and it’s been a year or so since I had one to actually look at directly.

I don’t know how the PCB is held into the pill. A hot air rework station might be the simplest way to make the swap, if you happen to have access to one (although not many DIY’ers do).