Yes - blueberries love peat moss and organic matter and mixing this along with dairy manure into potting soil should be a good addition. Just remember that peat moss can dry out and be hard to remoisten and blueberries love lots of water so don't let the soil dry out. I would mix the peatmoss and manure  half and half in a wheelbarrow before adding it to the potting soil. This way you won't get layers of just peat moss that could become dry. Keep growing, Marianne Binetti