I'm guessing that it could be done.....but I know I wouldn't attempt it. You'd have to route (sp?) out your design exactly the depth to match the thickness of the abalone (or whatever) you're going to put in there, or else it's not going to be level. Then you're going to want to cut the new abalone exact to match your cut outs. You'll have to put filler around all the edges if it's not an exact fit and sand it smooth. If you're a really, really good artist/woodworker you might have some luck, but it would scare the crap outta me to dig into my fretboard! I'm not too sure if it would change your sound or not....that's a good question.
I have one of those Turser Les Paul copies you see on ebay with the Serpent inlay on the neck. Looking at that, I just think a do-it-yourself-er would be getting in pretty deep. But then again, if you're really good with that kind of craft - you might be ok...and maybe even on the way to a new career!
You can always try to pick up a cheap old neck somewhere and give it a practice run.
