Let's assume that I am a decent JS programmer. I can easily do React.js development. I also can write HTML and CSS to some extent. I cannot, however, build a webpage from the ground up, i.e. define the HTML structure (say in terms of React components or just plain HTML), add some CSS and get the all-shiny responsive modern-looking fancy webpage. So, I work with a designer, who uses some sort of black magic (or maybe a WYSIWYG tool, or a service like wix.com) to prototype a web page.
So, what I get is a bunch of html files, images, css styles and maybe a bit of javascript.
Now I need to convert all this into a component hierarchy of React. I'm sure I can do this, and after the job is done, I get a shiny new website, beautiful from the technological and aesthetical point of view. However, we all know that we work in Agile environments. Later on, a designer wants me to change something. 'Add a black border' he says. And here things go out of control. Should I do this (manually look up the style in css and add a border)? What if changes required are more complicated? Like swap a header and a footer? Should he do this? (regenerate those source htmls/css/images again) What happens after that? Should I diff the whole website to learn what have changed and reimplement the whole component structure to reflect changes? Are there any accepted methodologies to solve this evil circle? Maybe a tool that maps the input ugly html code to the properly done React code? Or maybe I am totally wrong and I should learn the art of design myself?
Edit: Ok, as everybody is misundestanding the question, here is the shorter version. If the Templater changes the templates already implemented in React site, what can I do except manually diff and patch all the changes to the source css/html files?