import rhinoscriptsyntax as rs

def replaceLayerNames():
    layersL = rs.LayerNames()
    find = rs.StringBox("Which part of your Layer's name are you looking for?",None,"Find")
    replace = rs.StringBox("Replace with?",None,"Replace")
    if find and replace:
        newLayersL = []
        for layer in layersL:
            newLayer = layer.replace(find,replace)
            newLayersL.append(newLayer)
        
        for i in range(len(newLayersL)):
            new_name = rs.RenameLayer(layersL[i],newLayersL[i])
        return
    else:
        print "You did not enter search or replace word"
        return

replaceLayerNames()