Hi,
That's not a problem, at the end of the day it really depends on the nutrient values in the chicken manure based on how much should be added. I'm a fan of starting off light and then topdressing to add the necessary rest...
You don't need to worry about the pH value, as the soil life will regulate that, but you might want to let the mixed substrate sit for a week at the right moisture to activate and get the microbial life going.
Tips:
Kelp Meal
Alfalfa Meal
Basalt Flour
Dolomite Lime