I dont think there will be a problem .You might test a small area before applying over complete area. If you are having mildew or molding problems,can be caused by overhanging trees, especially nut bearing, or softwood trees. also, you need to get more attic ventilation, eve vents, soffit vents, power vents or turbines. what creates mildew is inside warm temps coinciding with outside cool air. need to equalize attic temps by adding more ventilation. the bleach water combo will only last a few weeks before returning to same status.

I thought they sell a concoction meant to clean your problem up. Check with your home center. I agree with toolcen2. Correct the problem before you waste the time of cleaning the shingles. It's never good for the shingles to stay wetter longer than necesary.

Good luck,
Devildog