Yes, as Steve: says, you can experiment on a small area and use the other solutions.
One last thing, now that I'm clear on your 'situation', IF you do as I described and you DON'T see an improvement, then the black spots are NOT mold - It's dirt. If it's mold, it will clean up.
Oh, to answer your questions about stains from the bleach, it's not like washing clothes which is cotton and the like. The shingles won't absorbe the mixture like you think. That's why it's OK to 'strengthen' the mixture if my initial recipe doesn't work. It doesn't really take much bleach in a gallon of water to kill the mold. Remember 2 things: 1) apply the mixture and let it sit for 10-15 minutes, and 2) wash along the bottom and work your way up the roof line to avoid streaking below. And rinse the current area you're working on AS WELL AS the areas 'below' that you already washed, each time you do a rinse.