Hey @Keita T., I think Process Flow Variables are supposed to be updated through the interface, like it indicates in the documentation. And I think it's built this way because Process Flow Variables are meant to be changed once before a model is run and the values are used through the run, instead of changing on the fly with FlexScript.
That being said, since there is a user interface to change a Process Flow Variable, there's probably a way to mimic the code that is used in the interface, although I haven't found how with a preliminary look at the tree.
It might be easier for your customer to link a Process Flow Variable to something like a Global Table, and then change the values in the Global Table with FlexScript.
Or if they just need to change something dynamically while the model is running, they could use Process Flow labels (or maybe labels on objects if using Object/Instance Process Flows).
