Not sure this qualifies as a hack, but it was fun to do.

If you're in the US, you likely have a few of the Harbor Freight special cheap LED lights, (up until recently) often free with a purchase of another item.  The older ones have 5mm LEDs for the smaller and larger light, newer versions feature COB LEDs for the larger light, but still use 5mm LEDs for the smaller light. I was in the mood to change the color on the smaller light so I cracked one open.

An interesting thing to note for this particular model, they actually bothered to use resistors for both the small and large lights. In some models, a resistor isn't even used for the larger LED light.  I did test the current on the larger led light. Using three AAA Nimh cells, it drives each LED at around 42 mA, a bit more current than I like. I may go back and put a higher value resistor later on.

An annoying thing I ran into, was that the PCB was heatstaked to the body.  In other models, it's just screwed into place. The crude solution was to use a lighter to soften the plastic and pull the PCB though, which worked surprisingly well. I then went on to replace the 10 ohm resistor with a 100 ohm resistor for the smaller LED light. I then swapped the white LEDs with green LEDs.

I used the lighter to redo the heatsteak, but it was a little loose. Oh well, not a big issue. I then closed everything up.  The smaller LED light draws around 11 mA of current, not bad.