I've used bleach successfully to bleach small areas ... I used a small paint brush. I needed to show depth to something (to make it appear round) so I bleached a small area of one side to show light, and applied black fabric ink to the other side to show dark - left the middle as it was. It turned out fantastic!
Again .. I used a diluted bleach (I think about 7 parts water to 1 part bleach) and painted it on with a small brush (the area I wanted bleached was perhaps 1/2" wide by the length of the fabric). My fabric was a batik in brown with a black print and it bleached to a lighter brown.
I wet the fabric first then I painted a small area at a time - perhaps 4" length X 1/2" wide. I let it stand on the fabric for as long as it took for me to visibly see a change, then I immediately ran it under cold water for a long time to thoroughly rinse all the bleach. If I needed it lighter, I repeated the method. When I was done with the whole piece I washed it with detergent in the sink and of course rinsed it again.
By wetting the fabric first I got a nice even bleed. Had I not pre-wet the fabric I would have had bleach "blotches".
Experiment!! Practice with the same fabric and try it both wet and dry to see which way works best for you.