The script is as follows:
arcpy.analysis.Buffer("siteboundary.shp","siteboundary1.shp","-5 Centimeters","FULL","ROUND","NONE",None,"GEODESIC")
arcpy.management.Delete("siteboundary.shp","ShapeFile")
arcpy.management.Rename("siteboundary1.shp","siteboundary.shp","ShapeFile")