It will definately change the guitar. The way Sims used to do it, and probably still do is that the hot and ground wires from the battery are fed through the pickup routes to the
neck joint. The fingerboard is cut very thinly on the side along the length of the neck and the LED's and wires are placed inside under the new
fret markers. The fingerboard is filled back in with the hot and ground connections placed at the heel of the neck to mate up with the connections from the battery, and viola!
You'll probably need a mini switch in your pickguard to turn it on and off, and you're set. Definately changes the "construction" of the guitar, but if you want the effect, that's how it's done. Sims do a great job, and I'd think it would only increase the value of your new guitar as well as making it more like Steve's.
Good luck, and welcome to Jemsite.