Currently I have some good design of grasshopper, which manipulating parameter able to produce variety of a product.
I have a thought, is that possible to convert my definition into something like a program? or a very user friendly UI so my client probably able to adjust the parameter easily and get the design he wanted?
Not that I know of. I was once looking for the same thing. You could use the remote panel in Rhino, where he can adjust sliders and bake in the Rhino window. That might make things easier.
In my experience (because I simply cannot comprehend how HumanUI works), it is easier to create your own GUI with WinForms, eto, WPF or whatever than to use HumanUI