Jeff,
Does this work for you?
Here is how this works. You take a family that you want to override and place it in the folder. You can place multiple families in there if you want to override this parameter for all of them. Use Directory.Contents to get all the family paths and feed that into Python node. Then also feed it a BuiltInParameter name as a string, and a value that you wan this parameter to be overridden to.
Hit Run and what will happen is that it will change that one parameter in the family, reload that family into the model silently and return that newly modified family.
Sounds like a plan?
Good luck!
