Bleach?
Umm...
Bleach?
Chlorine is the active ingredient? I used to work at a Pool Chemical shop, get chlorine on your pants and they go white. No biggy. Few weeks later it rots to become a hole. No biggy, they're pants. I'm pretty sure it'll have a similar effect on wood. However this comes without having tried it, so it may very well have no considerable side-effects...I'm not trying it until someone says they did it more than a month ago and says it hasn't affected their bass.
Sure its mold? Thats definitely one thing steer clear of on my bass, most molds need a pretty humid climate to survive, the kind of climate most necks don't survive. Try one of the other cleaning suggestions and see how it goes, if its into the wood you may need a light sand to get it out. Only if you're game, if it hasn't gotten noticably worse since you've owned it, its possibly mostly dead maybe, now it has character, little ones, microscopic ones.
Josh D