How to Conditionally Create a Parameter in Dynamo Only if It Doesn't Exist (Without Using Packages)

Actually no, there are posts to do similar thing but not creating parameters. Since I’m using “Parameter.CreateProjectParameter” node I can’t change any of the input like they did.
Run a node based on true false - Packages - Dynamo

Pop up in window for sequence in routine - Revit - Dynamo

Transaction.Start and Transaction.End - Revit - Dynamo

How can I determine the excution order of nodes? - Revit - Dynamo

Conditional execute - Revit - Dynamo

Run/Execute the whole script if it is true or else run/execute the other script - Revit - Dynamo