As Dan said, you could set it to Derived, that will show the "No parameters" message.
Alternatively, you can just reset the parameter's value in the updateParameters() method:
class Tool(object):
def __init__(self):
self.label = "Tool"
self.description = ""
self.canRunInBackground = False
def getParameterInfo(self):
return [
arcpy.Parameter(name="code", displayName="Land Use Code", datatype="GPString", parameterType="Required", direction="Input")
]
def updateParameters(self, parameters):
parameters[0].value = "9999 - Not Classifiable"
def updateMessages(self, parameters):
parameters[0].setWarningMessage("This parameter is for information only, you can't edit it.")
def execute(self, parameters, messages):
return
Have a great day!
Johannes