How to change variable values and get it's fitness like Galapagos

I want to develop a custom component which run my own muti-objective optimial algorithm. The most difficulty for me is how can I change variable values(like Number Slider) and get it’s result(fitness). I found many posts about this. But when I modify variables’ value, which result just show the latest change. There’s nothing I can do about it. Then, I know Galapagos platform from posts, it’s a great tool but can’t meet my need. So, the major point I want to know is how to change Number Slider value and get fitness in time like Galapagos.