I've just done this myself to one of my hilts, and will be posting a guide in the next week or so. You'll need a replacement switch, usually they come in 12mm or 16mm sizes. I believe the standard latching switch that US uses is about a 9mm or 10mm in diameter so you'd need to drill out the hole. Basically:
Pry out the switch
Cut the wires close to the contacts
Slide out the wiring, batteries, LED unit
Use a vice, clamp or other such equipment to hold the empty hilt in place
Using a power drill or something like that,
carefully widen the hole - a 12mm switch needs a 12mm drill bit, and so on
Replace the wiring in the hilt, and pull the severed wires back through the switch hole
Add some heat shrink to the cut wires
Strip the ends of the wires to expose the metal, and loop the exposed sections through the switch contacts. Twist them around themselves and slide the heat shrink over them, then heat them up to secure the connection
Add a bit of electrical tape wound around the thread of the AV switch to hold it in place, and slide the switch back in
The whole thing took me about half an hour - not too hard at all
