With the following Python script you can set the symbology of multiple layers to a predefined layer style. The script only works when running from th Python window in ArcGIS:
# Set layer that output symbology will be based on
symbologyLayer = (INSERT FILENAME SYMBOLOGY, for example: r"d:\ProjectsLocal\RMMOntgronding\hillshadeLayer1by1.lyr")
# lists layers to apply symbology to (you can use a wildcard here to only select a set of layers)
inputLayers = arcpy.mapping.ListLayers(arcpy.mapping.MapDocument("CURRENT"), "*")
# Apply the symbology from the symbology layer to the input layer
for layer in inputLayers:
arcpy.ApplySymbologyFromLayer_management (layer, symbologyLayer)
