Supplies: (should mostly be obvious)
LED Flashlight with diameter 1 1/8" or less
Soldering Supplies
Dremel/Hacksaw
Craft foam
Wire (if you can't salvage the original)
Pliers
Hotglue
Steps-
1. Open up your deploy and remove the front clip assembly
2. Remove the Screws holding down the Battery and light assembly, pull apart the original light:
image
3. Dissect your flashlight. I start by cutting it at the seam line, then 1/8th of an inch from the front to remove the lens. I used a pliers to remove the shiny silver piece, and then the Printed Circuit Board with the LEDs on it could be worked out the back.

What you need to retrieve:

4. Take that assembly and wrap it in craft foam. Then hotglue it into the original lens:

5. Now the fun part- wiring. I tried to salvage the original wiring but failed at striping it. If you payed attention it should be obvious, but here's a diagram for reference
Closeup of battery box and light:

Completed:

My little bro did the soldering, but now I understand it better and could do it next time.
Test it and put it back together. And your done! yah!
Before:

After:

But that really doesn't show the awesome difference it makes. If I ever needed it in combat I actually could use it now.

Super Clean

Super awesome
Another reason to wonder why hasbro doesn't do it like this stock.